Teacher: 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.
Teacher: Now, understand the problem? If you are still confused, see the following example:
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 _ .
Reason: It is clearly mentioned in the article that to the check effect of mood on children is the main purpose of the experiment.

Now, solve this instance: Article: There have been many great inventions that changed the way we live.The first great invention was one that is still very important today--the wheel.This made it easier to carry heavy things and to travel long distances.For hundreds of years after that there were few inventions that had as much effect as the wheel.Then in the early 1800's the world started to change.There was little unknown land left in the world.People did not have to explore much anymore.They began to work instead to make life better.In the second half of the 19th century many great inventions were made.Among them were the camera, the electric light and the radio.These all became a big part of our life today. The first part of the 20th century saw more great inventions.The helicopter in 1909.Movies with sound in 1926.The computer in 1928.And jet planes in 1930.This was also a time when a new material was first made.Nylon came out in 1935.It changed the kind of clothes people wear.The middle part of the 20th century brought new ways to help people get over disease. _ worked very well.They made people healthier and let them live longer lives.By the 1960's most people could expect to live to be at least 60.By this time most people had a very good life. Of course new inventions continued to be made.But man now had a desire to explore again.The world was known to man but the stars were not.Man began looking for ways to go into space.Russia made the first step.Then the United States took a step.Since then other countries, including China and Japan, have made their steps into space.In 1969 man took his biggest step away from the earth.Americans first walked on the moon.This is certainly just a beginning though. New inventions will someday allow us to do things we have never yet dreamed of.
Answer: 1850
Student:
Camera was invented after _ .