Given the task definition, example input & output, solve the new input case.
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.
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
Output: Researchers did experiments on kids in order to find out _ .
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 case for you: Article: People in Mutsuhito, Japan, lived through one hundreds, and sometimes thousands, a day.But they couldn't get used to it. What was it? It was a string of earthquakes that made the small town shake all the time.This went on for more than a year.Sometimes the quakes were very small.Only certain instruments could pick them up.At other times, the quakes damaged houses and land.The people were always afraid.They wished they knew how to stop the ground from shaking. People all over the world would like to know when an earthquake is coming.But an earthquake is almost always a surprise.Under the surface of the Earth, huge blocks of rock drift apart or slide against each other.The ground above splits apart or rumbles and shakes. Some scientists hope to predict quakes by keeping a close watch on animals.It seems that some animals can sense an earthquake coming.In 1969, animals in a Chinese zoo began to act funny one day.Swans flew out of their pond.A panda sat down, covered its eyes with its paws, and groaned.The animals seemed to know that something was about to happen.And it did.An earthquake struck.What was it that the animals sensed? Scientists are trying to find out. Keeping close track of the Earth's magnetic force in earthquake areas may also help.A few years ago, in Hollister, CA, scientists kept a record of the area's magnetic pull.For one week, the force grew stronger.Then it weakened suddenly.A day later, an earthquake struck. It may become possible to know when and where an earthquake will happen.But it will be much harder to stop one from happening. Many scientists think that the Earth's covering is not smooth.They say the earth's "skin" is made up of huge puzzle pieces called plates.Land and ocean floors make up these huge plates.Under the Earth's crust  , or plates, is hot rock.The plates float on top of this rock.Sometimes the rock forces its way through the crust.What happens then? A volcano is born! More often, the rock moves and forces the plates to pull away from each other, causing earthquakes to happen.(Volcanoes and earthquakes often go together.) Sometimes, the plates end up on top of each other.When this happens, the land above may look strange.Seen from the air, there seems to be a long scar in the Earth.This is called a fault  .The areas along faults have more earthquakes than other parts of the Earth. For now, we'll just have to shake along with the Earth.It goes through millions of small earthquakes every year.With luck, you won't feel a thing! 
 Answer: a volcano is born
Output:
When the rock forces its way through the Earth's crust,   _  .