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: Japanese sailor Kenichi Horie has finished a 110-day solo voyage across the Pacific Ocean in a boat pushed by sea waves to win another world first. Weak waves and ocean water movements made his arrival late, which was going to be in late May. "When waves were weak, the boat slowed down. That's a problem that needs to be solved," the adventure told reporters from his boat in western Japan. His 9.5-meter-long boat can move like a dolphin's tail, and it rises or falls with the waves. Horie reached his destination in the channel between the main Japanese islands just before midnight after covering about 7,000 kilometers from Hawaii. Horie first made world record in 1962 when, at the age of 23, he became the first person to sail alone across the Pacific. He made the three-month voyage from his hometown in spite of breaking Japanese law, which did not allow his citizens to sail on their own out of the country, and without a passport or money. He was arrested upon arrival in San Francisco but the city mayor freed him, gave him a 30-day visa and made him an honorary citizen. News of his achievement made him a hero back home in Japan and his book of the voyage In the Pacific was made into a film. Since then, he has completed many sailing trips across the Pacific and around the world. After his latest adventure with an environmentally friendly theme, Horie planned to return to his hometown on Sunday. He said, "Throughout history, mankind has used wind for power, but no one has appeared to be serious about wave power." Horie told the reporter, "I think I'm a lucky boy as this wave power system has remained untouched in fact."
Answer: sea waves
Solution:
Horie's boat was mainly powered by _ .