user: Problem: The sport remains dogged by allegations of doping, with Russia and Kenya facing bans from this summer's Olympics for failing to tackle cheating athletes.
But UK Athletics chief De Vos said: "I think we're through the worst of it.
"I think without doubt 2017 will be the cleanest championships ever."
De Vos, 49, added: "I would be very hopeful 2017 will be a very clean games but it's impossible to say with certainty and that's a shame."
Russia was suspended from world athletics in November and must now convince the sport's governing bodies it has reformed its doping polices to be reinstated at the Olympics.
Three IAAF officials were banned for life in January for breaching anti-doping rules while Kenya has missed two deadlines to prove it can combat drug-taking.
What was that article about?

A: Athletics has "come through the worst" of its doping problems and the London 2017 World Championships will be the "cleanest ever", according to the event's director Niels de Vos.


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The 27-year-old from Newtownards, County Down, becomes the first Irishman to win a gold medal at the championships for 117 years.
Irvine won his silver medal in the  individual pursuit which was won by reigning champion Michael Hepburn.
Less than an hour later, Irvine sensationally won the 15km men's scratch race in Minsk, Belarus.
The Irish competitor accelerated clear of the field with 10 of the 60 laps to go and managed to hold off his rivals in the finale.
Irvine is the first Irish male competitor to win a medal at the World Cycling Championships since Harry Reynolds took the one-mile amateur title in 1896.
Reynolds also won a bronze a year later.
In 2012, Caroline Ryan won Ireland's first modern World Championships medal with bronze in the women's points race.
In the individual pursuit, Irvine's time of four minutes and 22.53 seconds was a couple of seconds down on the time he had in reaching the final.
Australian Hepburn, 21, built up a big lead and almost caught Irvine coming to the end of the 4km race.
Irvine just had time to receive his medal, change his race numbers and return to the bike before his gold success in the scratch race.
The championships in Belarus represent a significant breakthrough for Irvine.
The Ulsterman won silver medals in the scratch race and the individual pursuit at the Track World Cup in Glasgow in November.
Irvine competed for Northern Ireland at the Delhi Commonwealth Games and was 13th in the multi-discipline omnium event at last year's London Olympics.

Sum: Martyn Irvine has made Irish cycling history by winning gold and silver at the World Track Championships.


Q: Waste water teams from Severn Trent Water will be visiting Welshpool to speak to people about what they should and should not flush down the toilet.
The company said since 2011 it had dealt with 143 blockages in the Oldford Rise, Oldford Close and Berriew Road areas.
A majority of the blockages were caused by sanitary products becoming stuck.
So-called "flushable" wipes were another major cause of blockages, the company said.
Jacqueline Whitehead, customer and community lead for Severn Trent said: "We know that there are certain areas in our region where sewer blockage numbers are much higher than anywhere else.
"Welshpool is one of those places.
"Sewer flooding is one of the most horrible things that can happen to our customers and we don't want people to suffer in this way - it's entirely preventable. "The education programme has been planned for Monday and Tuesday

A: Residents in a "sewer blockage hotspot" in Powys are to be given advice on improving their flushing habits.


Text: Persistent rain in the capital saw play abandoned at 15:30 BST.
However, Surrey's title challengers Lancashire also saw the opening day against Essex abandoned at Chelmsford.
Surrey, who have already won promotion along with the Red Rose county, need 17 points to guarantee going up as champions.
Victory for Northants could see them finish third if Essex fail to win nine points.
summary: Surrey's quest to clinch the Division Two title remains in tact despite rain washing out day one of their match against Northants at The Oval.


Question:
Article:The allegations concern institutions in Yorkshire, London, Manchester, Kent, Surrey and Devon, among others, and relate to the 1960s, 70s and 80s, the Department for Education said.
The information was uncovered as part of a review by the Met Police.
Police have said Savile abused more than 200 people over six decades.
The former BBC DJ and presenter died in October 2011, aged 84, before the sex abuse allegations came to light.
The organisations include a school for the blind in Harrogate, two schools and a children's home in Savile's birthplace of Leeds, and a Barnardo's children's home in Redbridge, north-east London.
In a written statement, Education Secretary Michael Gove said: "This information was uncovered as part of the document review process undertaken by the Metropolitan Police Service on behalf of the Department of Health.
"Having reviewed the information, I have decided that the Department for Education should pass the information to the appropriate organisations for further investigation.
"In most cases the work will be conducted by the relevant local authority; in others the relevant institution or a legacy organisation will take the lead."
In January 2013, a Metropolitan Police report said Savile had been a "prolific, predatory sex offender" who was able to "hide in plain sight" while abusing his victims.
A second report said he could have been prosecuted in 2009 if victims had been taken more seriously.
A criminal investigation, Operation Yewtree, was launched in October 2012.
The NHS is already investigating 33 hospitals' links with Savile after police passed information to the Department of Health.
Mr Gove said the new inquiries, which will be overseen by human rights lawyer Lucy Scott-Moncrieff, would follow the same arrangements.
Henshaws Society for Blind People, in Harrogate, said in a statement: "It is right that steps are taken to explore these allegations, to find out what happened and why, and we will be providing what evidence we can to the inquiry and will be putting as much effort as it takes into providing the inquiry with the information they need."
Action for Children, which ran the Penhurst School in Oxfordshire before it closed in May 2013, said it had been told of the allegations on Tuesday.
It said: "We are co-operating with the Department for Education and will conduct a full investigation into Savile's possible visits to our former school in the 1970s."
Gloucestershire County Council said it would do everything in its power to find out what had happened at Parklands Children's Home, which closed in 2002.
In his statement, the education secretary named the following institutions:
Source: Department for Education

Summarize the main points of that article.
Answer:
Claims Jimmy Savile abused children at 21 children's homes and schools in England must be investigated by local authorities, the government has said.


Text: The case against 43-year-old Richard De Wit, from the Netherlands, resumed earlier in Kashmir after a succession of adjournments.
He is accused of the multiple stabbing of Ms Groves on a houseboat on Dal Lake in Srinagar in April.
At the latest hearing, the prosecution presented Abil Shoda, a Kashmiri who gave evidence through an interpreter.
He said Ms Groves was not just a guest in the houseboat, but a part of the family.
She had said goodnight to family members on the night of her killing before retiring to her room, he said.
No witness heard during the trial has yet reported having seen the killing take place.
Many of the adjournments have been caused by the judge's dissatisfaction with the police handling of the alleged murder weapon - a knife with a broken blade.
The next trial date has been set for 25 November.
summary:

assistant: The trial of the man accused of killing Guernsey woman Sarah Groves has heard evidence from her boyfriend's uncle.