Question: Which two Doctors met in "Time Crash"?
About the article "Doctor Who", section "Charity episodes".

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Due to time travel, it is possible for the Doctor's various incarnations to encounter and interact with each other, although this is supposed to be prohibited by the First Law of Time (as stated in "The Three Doctors") or permitted only in the "gravest of emergencies" ("The Five Doctors").
In the 1963–1989 television series, such encounters were seen on three occasions, in "The Three Doctors" (1972), "The Five Doctors" (1983) and "The Two Doctors" (1985).
In "Day of the Daleks" (1972), the Third Doctor and Jo Grant very briefly met their future selves due to a glitch during a temporal experiment (the serial was supposed to end with the same scene depicted from the perspective of the "other" Doctor and Jo, but was excised because it was anticlimactic).
In "Father's Day" (2005), the Ninth Doctor and Rose observed but did not interact with past versions of themselves; when Rose changed history, the earlier selves – after momentarily noticing Rose running past – vanished and a temporal paradox was created that attracted the extradimensional Reapers.
The Tenth and Fifth Doctors met in the TARDIS in the mini-episode "Time Crash", which aired on 16 November 2007 as part of the BBC's annual "Children in Need" appeal.
This marks the first time the Doctor has met a previous incarnation since the show's revival.
Although the scene aired outside the series itself, it was established as taking place between the events of "Last of the Time Lords" and "Voyage of the Damned.
"The BBC novel "The Eight Doctors" was written by respected Doctor Who writer Terrance Dicks, the same author who wrote "The Five Doctors".
In it, he tries to reconcile the continuity errors of the 1996 movie, while having the Eighth Doctor meet and interact with each of his previous selves.
Physical contact between two versions of the same person can lead to an energy discharge that shorts out the "time differential".
This is apparently due to a principle known as the Blinovitch Limitation Effect, and was seen when the past and future versions of Brigadier Lethbridge-Stewart touched hands in "Mawdryn Undead".
Oddly, the Doctor's incarnations do not appear to suffer this effect when encountering each other and shaking hands.
This has never been explained.
An essay in the "About Time" series by Lawrence Miles and Tat Wood suggests that Time Lords are somehow exempt from the effect by their very nature.
Rose Tyler is seen holding an infant version of herself in "Father's Day", with no visible energy discharge, but the contact does allow the Reapers to enter the church in which the Doctor and several others are taking refuge.
While doing a live commentary on the episode at the 2006 Bristol Comic Expo, episode author Paul Cornell said that this is supposed to be due to the Blinovitch Limitation Effect, even though it is not mentioned by name.
He also suggested that the lack of a spark may be down to the fact that the Time Lords were no longer around to manage anomalies.
The interaction of the Doctor's various incarnations produces a continuity anomaly that requires suspension of disbelief on the part of viewers, as one may assume that his past selves would forget that he would later regenerate.
In "Castrovalva", the newly regenerated Fifth Doctor clearly indicates that the outcome of his regeneration cannot be predicted; however, the Fifth Doctor should have had memories from his earlier incarnations of having met himself per the events of "The Two Doctors" and "The Five Doctors".
Also, the Second, Third and Fifth Doctors should be already familiar with the events of "The Five Doctors", having already lived through them multiple times.
It has been suggested in fandom that the Time Lords erase the Doctor's memory after such encounters (and in "The Two Doctors" there is mention of Dastari administering to the Second Doctor a drug that he bemoans "affects the memory"); the novel "The Empire of Glass" features the First Doctor directly after his return from the events of "The Three Doctors", his memory of the adventure having been totally erased barring a vague recollection of meeting "a dandy and a clown".
In the 2006 episode "School Reunion", the Tenth Doctor and Sarah Jane Smith both seem to indicate in dialogue that they haven't seen each other since her departure from the TARDIS in "The Hand of Fear", although this contradicts their having met later during "The Five Doctors".
She, in that story, does not realise that the Fifth Doctor is a later incarnation of the third and fourth Doctors with whom she had previously travelled.
In "Time Crash", the Tenth Doctor remembers and reproduces what he saw himself do when he was the Fifth Doctor, a fact that seems to surprise the Fifth Doctor himself.
Russell T Davies has expressed a dislike for stories in which multiple incarnations of the Doctor meet, stating that he believes they focus more on the actors than on the story itself.
In 2007, David Tennant showed enthusiasm for the idea of a multi-Doctor story, but expressed doubts about the practicality of shows involving multiple previous Doctors, given that three of the actors who played the character were deceased.
Since the series revival, there have been two multi-Doctor stories, the "Children in Need" special "Time Crash" and the 50th anniversary special, "The Day of the Doctor".
Before that, the only references to past incarnations (from 1963 to 1996) have been in the aforementioned episode "School Reunion" (in which the Doctor acknowledges having regenerated "half a dozen times" since last seeing Sarah Jane) and in drawings that the Doctor (who has temporarily become human to hide from the Family Of Blood) makes based on dreams of his other life in the 2007 episode "Human Nature".
Seen on screen are the First, Fifth, Sixth, Seventh and Eighth Doctors, but a fuller view briefly available on the BBC website depicted all ten incarnations.
However, in the 2008 Christmas episode, The Next Doctor, the Tenth Doctor discovers an info stamp originally held by the Cybermen, which includes images of all his past selves.
This is a clear affirmation of his past, and that the (then) current incarnation was indeed the Tenth.
This was reaffirmed in the episode "The Eleventh Hour", when the Doctor asks the Atraxi whether this planet is protected.
The Atraxi then shows 10 images, one of each Doctor from the first to the tenth, with the eleventh walking through the image of the tenth at the end.
This is also confirmed in the episode "The Lodger", when the Doctor, explaining to Craig who and what he is, points at his face and says, "Eleventh.
"Because each new Doctor is different from his previous incarnations, how their personalities interact varies when two or more different incarnations encounter each other.
"Time Crash" featured Peter Davison returning as the Fifth Doctor.
This event is explained as occurring due to the current Doctor having left his shields down when rebuilding the TARDIS following "Last of the Time Lords" and then accidentally crossing the Fifth Doctor's timeline, allowing the two TARDISes to merge.
When the Tenth Doctor effortlessly averts the impending Belgium-sized hole in the Universe caused by this temporal anomaly, he reveals having known what to do because he saw himself do it as the Fifth Doctor and remembered.
He goes on to tell the Fifth Doctor how fond he was of his incarnation and how he influences the current Doctor's personality.</ref> However, in their two meetings, the Second Doctor and Third Doctor had a degree of antagonism towards each other, with the patriarchal First Doctor critical of them both.
During the Virgin New Adventures, the Seventh Doctor was occasionally at odds with his subconscious memory of his previous incarnation as his memory of his past self became increasingly associated with the Valeyard, his dark, future self, but he eventually accepted his dark side and 'reformed' his memory of his former self, although it was never established how the two Doctors would interact if they had met in person.
On many occasions the Eleventh Doctor has actually encountered himself from a different point in his timeline: in "The Big Bang", the mini-episodes "Time" and "Last Night", and in "Journey to the Centre of the TARDIS", at the end, the Doctor interacted with his past self to reset time, by giving himself a device that helps get the TARDIS to escape the salvagers' magnetic beam before they can activate it.
In all stories, multiple versions of the Eleventh Doctor from different timelines meet and carry on brief conversations.
Additionally, the Eleventh Doctor encountered an artificial (though physically and mentally identical) copy of himself in "The Almost People", fought against "Mister Clever", an artificial personality generated out of his own by the Cybermen in "Nightmare in Silver", and was pitted against "The Dream Lord", a manifestation of his self-loathing and anger, in "Amy's Choice".
Late, the Eleventh Doctor entered his own timeline in "The Name of the Doctor" to rescue his companion Clara Oswald, and while there observed a past incarnation portrayed by John Hurt, one whose actions caused him to be unworthy of the name "Doctor" and viewed as shameful by his future selves.
In the 50th anniversary special, "The Day of the Doctor", the Eleventh Doctor encounters both the Tenth Doctor and the War Doctor (played by John Hurt).
The Tenth and Eleventh Doctors are generally amicable towards each other, despite some bickering, although the War Doctor treats them both as behaving too childishly.
Despite this, he does come to admire both of his future incarnations, working together with them and eventually choosing to go through with the act of destroying Gallifrey because he knows it will help them become what they are.
The Tenth and Eleventh are initially somewhat leery of the War Doctor, the Eleventh describing him as the "one life I have tried very hard to forget."
However, both of them later recognize that the War Doctor followed what seemed to be the only course open to him, and are even willing to help him carry it out so that he won't have to suffer the guilt alone.
Fortunately, with some influence from the Moment-a sentient Time Lord weapon that brought about their meeting-the three are able to stumble upon an alternative: sending Gallifrey into a pocket universe, making it seem as though it has been destroyed.
The three are then joined by the other nine previous Doctors and the future Twelfth Doctor (Peter Capaldi) in this act.
The Eleventh Doctor is also shown to have memories of these events, but only recalls them after they have begun.
This is explained as an instability in the timeline, which causes the War and Tenth Doctors to forget their meeting, thus maintaining the continuity in which the Doctors from the War Doctor on believe themselves to have destroyed Gallifrey. 
There was one fatality, Mbuyu Mibanga, a deputy in the National Assembly of the Democratic Republic of the Congo.
At least 12 more were injured, including two Congolese doctors working for the World Health Organization. 
 This story is a sequel to "Hornets' Nest" and "Demon Quest", with the Fourth Doctor, Yates and Mrs Wibbsey reuniting.
"Serpent Crest" begins by picking up from the cliffhanger at the end of "Demon Quest".
The Fourth Doctor mentions that the Time Lords removed certain events from his memory, just before they force regenerated him at the end of "The War Games".
In particular, they hid memories of adventures he had with his other incarnations.
The Second Doctor encountered his previous and following selves in "The Three Doctors".
He met them again in "The Five Doctors", along with the Fifth Doctor.
He also met the Sixth Doctor in "The Two Doctors".
The Fourth Doctor investigates his past by checking his 500 Year Diary, which was seen with the Second Doctor in "The Power of the Daleks" and "The Tomb of the Cybermen".
The visiting Doctor recalls his adventures with the Cybermen in "The Invasion" and "The Tomb of the Cybermen", the Yeti in "The Web of Fear" and the giant crabs in "The Macra Terror".
He also mentions an encounter with the Daleks in the diamond mines of Marlion, as mentioned in the Paul Magrs novel "Verdigris".
The Doctor met the real Rasputin in the novel "The Wages of Sin" and the audio drama "The Wanderer".  
With the release of Crash Bash, Vivendi Universal's publishing deal with SCE had ended, and Crash's prominent status within the video game community prompted the company to make Crash a multiplatform series.
Giving the series to Mark Cerny and Vicarious Visions to develop two separate but connected games.
"Crash Bandicoot: The Wrath of Cortex" was originally in development by Travelers Tales.
After a falling-out between Vivendi Universal and the two entities, Traveller's Tales was forced to alter the game from a free-roaming title to a standard "Crash" title.
Traveller's Tales had to begin development of the game from scratch and were given only twelve months to complete the game.
The game received mixed reviews but made the Greatest Hits lineup due to strong sales.
Despite the rights of Crash Bandicoot going to Vivendi Universal, Sony still retained the rights for the distribution and porting of the original Crash Bandicoot game series.
The following year, Vivendi would have Vicarious Visions release their first Crash Bandicoot game, a handheld exclusive called was developed by Vicarious Visions and released to favourable reviews.
The game would be noted for being extremely similar to Naughty Dog's Crash Bandicoot 3.
This would warrant a sequel, , which would also be met to similar reception.
During this time a subsidy of Traveller's Tales - Traveller's Tales Oxford Studio were developing a new Crash game for console.
This game was to be Crash Nitro Kart but due to unknown circumstances Vivendi moved development of Crash Nitro Kart over to Vicarious Visions.
Traveller's Tales Oxford Studio then moved on to their next project, Crash Bandicoot Evolution.
Crash Bandicoot Evolution was set to create a new form of gameplay for Crash with the game planned to be a Platformer/RPG with many different elements planned for the game; it eventually became Crash Twinsanity.
Although Traveller's Tales planned on creating a Crash Bandicoot game titled "Cortex Chaos", Vivendi never picked up the game, effectively cancelling it.
Vicarious Visions's fourth and final game was for the Game Boy Advance. 
As Meredith nervously awaits a final decision from Derek, her fear is interrupted when a train crash brings several seriously injured patients to the hospital, including Bonnie and Tom, a pair of passengers who’ve been impaled on a metal pole.
The only way to remove the pole from these two is a very risky surgery where one of the two must be slid back on the pole, more than likely causing them to die.
Tom, an older man in his 50s, offers to give his life to save Bonnie because he is older and has had a shot at living.
Bonnie, an attractive woman in her late 20s, is engaged to be married and waiting for her fiancé to arrive at the hospital.
Since Bonnie's injuries are determined to be worse than Tom's, she is the one chosen to be moved on the pole.
All the doctors involved in the surgery promise they will do everything they can to try and save both Bonnie and Tom.
In surgery, after being removed from the pole, Bonnie begins to crash.
Doctors work on her only for a short time before they deem her "unsavable" and turn to help Tom, who has a greater chance of living.
As the doctors move to Tom, Meredith stays by the dying Bonnie saying "What about her?
We can't just abandon her!"
This particular situation parallels Meredith's situation with Derek.
She feels that she has just been dropped when Derek returns to his unfaithful wife.
At the emergency department, Alex is doing sutures but eventually fails to notice a woman bleeding internally which leads to her death.
In the mean time, Addison Shepherd sees great potential in Izzie, who must decide whether her loyalty as Meredith’s friend outweighs professional gain.