You will be given a definition of a task first, then an example. Follow the example to solve a new instance of the task.
In this task, you're given an article and an answer. Your task is to generate the fill-in-the-blank question for this answer based on the given article. The blanks are always at the end of the question, and can be filled with more than one word or phrase.

Article: Homework can put you in a badmood , and that might actually be a good thing. Researchers from the University of Plymouth in England doubted whether mood might affect the way kids learn. To find out the answer, they did two experiments with children. The first experiment tested 30 kids. Someshapes were hidden inside a different, larger picture. The kids had to find the small shapes while sitting in a room with either cheerful or sad music playing in the background. To test their mood, the scientists asked the kids to point to one of five faces, from happy to sad. Children who listened to cheerful music tended to point to the smiley faces while the others pointed to the unhappy ones. The researchers found that sad kids took at least a second less to find the small shapes. They also found an average of three or four more shapes. In the second experiment, 61 children watched one of two scenes from a film. One scene was happy, and the other was sad. Just like in the first experiment, kids who saw the sad scene acted better compared to the others. The researchers guessed that feeling down makes people more likely to focus on a problem or difficult situation. Not all scientists agree with them, however. Other studies argued that maybe, that cheerful music in the first experiment distracted kids from finding shapes. While scientists work on finding out the answers, it still might be wise to choose when to do your tasks according to your mood. After eating a delicious ice cream, for example, write an essay.
Answer: whether mood affects their learning ability
Solution: Researchers did experiments on kids in order to find out _ .
Why? It is clearly mentioned in the article that to the check effect of mood on children is the main purpose of the experiment.

New input: Article: April Fool's Day , was a day of laughing and jokes. This day is kept in many countries, not only in Britain and the USA. This is a day to play jokes and make people laugh. Nobody knows when was the beginning of this custom. Some people connect it with the end of winter and the return of spring which make people merry and ready to play jokes. In Scotland young people were sent for hen's teeth or bird's milk and everybody laughed when they could find such things. In the USA and Britain some people could place a sign on a person's back with the words "push me!" Children often tell a grown-up that his sock is torn or he has something black on his face, and then shout "April Fool!" There is also the old purse trick. A purse is left lying in the street, but when someone wants to take it, it is quickly pulled back by a string which the hidden joker holds in his hand. Or the purse may be filled with stones. Sometimes invitations are sent to people, asking them to come and visit somebody, but when they come they see that nobody expects them. Some people like to telephone to the zoo on the day and ask for Mr. Fish, Miss Fox or Mrs. Cat. All these jokes are very old but still they make people laugh.
Answer: Someone
Solution:
_ knows when the custom of April Fool's Day started.