instruction:
Given a context passage, generate a question from the passage such that its answer is shortest continous span from the passage.
question:
Twisted Obsession (original Spanish title: El sueno del mono loco, literally The Dream of the Mad Monkey) is a 1989 Spanish erotic thriller directed by Fernando Trueba, starring Jeff Goldblum and Miranda Richardson.
answer:
Which is the basis of Twisted Obsession?


question:
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
answer:
What is Anna's dad occupation?


question:
By the mid-nineteenth century, the term "icebox" had entered the American language, but ice was still only beginning to affect the diet of ordinary citizens in the United States. The ice trade grew with the growth of cities. Ice was used in hotels, taverns , and hospitals, and by some forward-looking city dealers in fresh meat, fresh fish, and butter. After the Civil War (1861-1865), as ice was used to refrigerate freight cars, it also came into household use. Even before 1880, half of the ice sold in New York, Philadelphia, and Baltimore, and one-third of that sold in Boston and Chicago, went to families for their own use. This had become possible because a new household convenience, the icebox, a precursor of the modern fridge, had been invented. Making an efficient icebox as not as easy as we might now suppose. In the early nineteenth century, the knowledge of the physics of heat, which was essential to a science of refrigeration, was rudimentary . The commonsense notion that the best icebox was one that prevented the ice from melting was of course mistaken, for it was the melting of the ice that performed the cooling. Nevertheless, early efforts to economize ice included wrapping up the ice in blankets, which kept the ice from doing its job. Not until near the end of the nineteenth century did inventors achieve the delicate balance of insulation and circulation needed for an efficient icebox. But as early as 1803, and ingenious Maryland farmer, Thomas Moore, had been on the right track. He owned a farm about twenty miles outside the city of Washington, for which the village of Georgetown was the market center. When he used an icebox of his own design to transport his butter to market, he found that customers would pass up the rapidly melting stuff in the tubs of his competitors to pay a premium price for his butter, still fresh and hard in neat, one-pound bricks. One advantage of his icebox, Moore explained, was that farmers would no longer have to travel to market at night in order to keep their produce cool.
answer:

What was essential to to make an icebox efficient according to the passage?