Given a question and a context passage, generate the answer having the word or phrase from the context passage. Here, the answer should be a shortest continous span from the passage.

Example Input: Context: Anna Foster (Mandy Moore) is the daughter of the President of the United States, James (Mark Harmon) and First Lady Michelle Foster (Caroline Goodall).When a hassle of Secret Service agents ruins a first date, Anna demands some freedom. Her dad agrees to send only two agents with Anna and Gabrielle La Clare (Beatrice Rosen) to a concert when Anna goes to Prague with her parents. A sexy new look for Anna causes her father to renege. When Anna discovers the concert is filled with agents and that her father has broken his promise, Gabrielle helps Anna elude her protectors. Outside the concert, Anna meets Ben Calder (Matthew Goode), and asks him to drive her to escape the agents. Anna goes to a bar with Ben and proceeds to get drunk. Unbeknownst to Anna, Ben is with the Secret Service, and tells agents Alan Weiss (Jeremy Piven) and Cynthia Morales (Annabella Sciorra) where Anna is. The President orders the three agents to have Ben guard Anna without telling her who he really is, to give her an illusion of freedom with a guarantee of safety. Believing herself free of her guards for the first time in years, Anna jumps into the Vltava River naked, mistaking it for the Danube, and Ben has to fish her out (he stays clothed). Weiss and Morales buy the camera from someone taking pictures of the skinny-dipping Anna. Anna and Ben climb a rooftop to watch an opera being shown in a plaza, where Anna eventually falls asleep with Ben guarding her, and Weiss and Morales watching from another roof.The next morning, Anna calls her parents to avoid getting into further trouble with them. Knowing she is safe, her father is initially indulgent, and Anna is about to return, but his tone changes when he is shown the photos of her nude in the river. The First Lady, however, asks, "What happened to 'let freedom ring?'" (That had been his earlier line when he had decided to let her stay out with Ben.) Anna is outraged at both her dad's sudden imperious tone and finding out that he traced her call. She decides to meet Gabrielle at the Love Parade in Berlin and return to her parents right before the plane trip home. Ben goes with her on the train, where they meet Scotty McGruff (Martin Hancock), a flighty romantic obsessed with Six Million Dollar Man stickers and the interconnectivity of the world, he gives them a stack of stickers and tells them to stick them up in random places, then one day when they are unhappy, they will see one and it will make them smile. Through him, the two learn that they have boarded a Venice-bound train. When they arrive in Venice, Ben calls the other agents to tell them where they are but has to leave the phone dangling when he realizes he can no longer see Anna. He finds her and McGruff getting new clothes, and the three explore Venice - until McGruff steals their wallets. Ben is about to tell the cafe they cannot pay when Anna is recognized and races off to avoid being identified as the First Daughter. Ben follows, and they tell a story of marrying, against the wishes of Anna's parents, to get a gondola ride from a kind-hearted gondolier, Eugenio (Joseph Long). Ben kisses Anna during the ride to hide her from the cafe staff's sight. Since they have no place to stay, Eugenio invites them to his and his mother Maria's (Miriam Margolyes) house. That night, thinking the kiss meant that Ben cares for her, Anna offers herself to him. To dissuade her, Ben is disingenuous and harsh. Anna finally gets in the bed alone, while Ben lies on the floor.The next day, Eugenio drives them to the Austrian border, as Weiss and Morales show up at Maria's looking for the gondolier with whom Anna and Ben were last seen. Maria tells them that Anna and Ben are married, which is reported to Anna's parents. Upset that Ben rejected her, Anna gets a ride on a truck, leaving Ben to 
 Question: What city are Ben and Anna in?
Example Output: london

Example Input: Context: The movie opens with Ralph Wiggum singing along to the 20th Century Fox logo. We then cut to Itchy & Scratchy: The Movie. They are out on the moon. Itchy kills Scratchy and then returns to earth and is painted as a hero by the media. Shortly thereafter, Itchy is elected president. Later as Itchy is in the White House, he sees a supposedly dead Scratchy on the moon. Scratchy holds up a sign that says "I'm telling", which freaks President Itchy out. Itchy then retaliates by sending a hundred missiles toward Scratchy. This is then seen in the theater which is being attended by the Simpsons. Homer stands up and yells "Boring!". Lisa replies "Dad, we can't see the movie!". Homer then goes off on a tirade about why they're paying to watch something in the theater that they normally watch on TV, and that everyone in the audience is a gigantic sucker, especially you. Cue a very fancy and stylized version of the standard Simpsons opening theme.The opening ends with Green Day hosting a concert at Lake Springfield (Singing the Simpsons theme after the opening credits). After they finish their song, they talk about the environment. The audience becomes angry and begins to throw garbage at them polluting the lake and causing their barge to dissolve and sink, killing them. The next day at church, while they have a short memorial for Green Day, Grampa is possessed by God warns the city of a future disaster. Marge believes Grampa's prediction, and decides to work out the meaning of the message. Meanwhile, Lisa starts to talk about the environment, with no success. She encounters Colin, an Irish boy who shares the same passions as her. Homer gets a note from Marge of his chores, and one is fixing the sinkhole. Instead of fixing it, Homer puts Maggie's sandbox over it. His next chore is to fix the roof. While repairing the roof, Homer and Bart decide to have a dare contest. Homer dares Bart to climb the antenna. Bart does so, and gets stuck. Homer shakes it in order to get Bart down. Homer dares Bart to skateboard to Krusty Burger naked, which Bart object's to, saying girls will see his "doodle". After Homer threatens to call him chicken for the rest of his life, Bart agrees. Bart becomes stuck naked on the window of the building. After he is apprehended by the police, and tied to a Stop sign pole, Homer turns up and they decide to order a meal, he brings him socks and a shirt, and no pants. Inside the restuarant, Ned Flanders helps Bart out by giving him a pair of pants, and understands his feelings which begins a relationship and mutual respect between the two. Meanwhile Krusty is filming a commercial. When recording finishes Krusty orders for the pig he is using in the commercial to be slaughtered, causing it to flee to Homer who adopts him, and calls him Spider-Pig. That evening Lisa holds a conference at city hall, called "An Irritating Truth" and explains that the town lake cannot sustain anymore pollution. Mayor Quimby declares a state of emergency and orders the cleansing and protection of Lake Springfield.They put up a fence around the lake to halt further dumping, and announce it is idiot proof, using Cletus as an example to try to throw a possum in the lake, and fail. Soon, Marge asks Homer where "Spider-Pig's/Harry Plopper's" waste is going. Homer shows her an overflowing silo, asking how a pig can fill it up in two days, Homer replies that he helped, horrifying Marge who tells Homer to dispose of it safely. While waiting in a queue at the dump Homer is told by Lenny that Lard Lad Donuts has been shut down and that they are giving away free donuts. Homer, in his haste to get to the giveaway decides on a quicker means of disposal and dumps the silo into the lake, causing it to become heavily polluted. A nearby squirrel jumps into it and becomes severely mutated, with many eyes. Nearby, 
 Question: What do Lisa and Colin convince the entire town to clean?
Example Output: the lake

Example Input: Context: In the 1950s, a family that owned a farm near Beulah, Michigan kept a bull chained to an elm . The bull paced around the tree, dragging the heavy iron chain, which led to a groove in the bark . The groove deepened over the years. Though for whatever reason, it did not kill the tree. After some years, the family took their bull away. They cut the chain, leaving the loop around the tree and one link hanging down. Then one year, agricultural disaster struck Michigan in the form of Dutch Elm Disease. All of the elms lining the road leading to the farm became infected and died. Everyone thought that the old elm would be the next. The farm owners considered doing the safe thing: pulling it out and cutting it up into firewood before it died. But they simply could not bring themselves to do it. It was as if the old tree had become a family friend. So they decided to let nature take its course. Amazingly, the tree did not die. Nobody could understand why it was the only elm still standing in the county! Plant experts from Michigan State University came out to observe the tree. They observed the scar left by the iron chain, now almost completely covered by bark. The experts decided that it was the chain that saved the elm's life. They reasoned that the tree must have absorbed so much iron from the chain that it became immune to the virus. It's said that what doesn't kill you will make you stronger. Or, as Earnest Hemingway put it, "Life breaks us all, but afterwards, many of us are strongest at the broken places." 
 Question: What actually saved the elm?
Example Output:
the iron chain.