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.

[EX Q]: Article: In some parts of the United States, farming is easy. But farming has always been difficult in the northeastern corner of the country, which is called New England. New England has many trees and thin, rocky soil. Anyone who has wanted to start a new farm there has had to work very hard. The first job has been cutting down trees. The next job has been digging the stumps of the trees out of the soil. Then the farmer has had the difficult job of removing stones from his land. This work of removing stones never really ends, because every winter more stones appear. They come up through the thin soil from the rocks below. Farmers have to keep removing stones from the fields. Even today, farms which have been worked on for 200 years keep producing more stones. That is why stone walls are used instead of fences around New England fields. The stone walls are not high; a man can easily climb over them. But they keep the farmer's cows from joining his neighbor's cows.
Answer: why there are many stone walls in New England
[EX A]: This selection explains _ .

[EX Q]: Article: Many people have wondered what makes the oceans rise and fall on the word's beaches twice a day. Those tides are caused by the force of the Moon's gravity and the rotation of the Earth. Gravity acts on the center of any solid object. The Earth is mostly molten rock, but compared to the oceans, we can think of it as a solid object. As you know, the oceans are fluid and lie on the surface of the Earth. When the Moon is overhead, the oceans are four thousand miles closer to the Moon than the Earth's center is. Because the oceans are closer, the Moon pulls harder on the water than on the Earth. This stronger pull makes the water bunch up a little under the Moon, creating a high tide. At the same time, the oceans on the opposite side of the Earth are four thousand miles farther from the Moon than the Earth's center is. The Moon's pull on this water is weak. This water bunches up because it is "left behind"(making another high tide) as the Earth is pulled slightly towards the Moon. When the waters bunch up on these two sides of the Earth, they draw water away from the other sides of the Earth, which creates the low tides. As the Earth rotates, different parts of the land and oceans pass through the high-tide and low-tide zones. And that makes the waters on our coasts go up and down.
Answer: Moon's gravity or Earth rotation
[EX A]: According to the passage, there would be no tides if there were no _ .

[EX Q]: Article: Early in the 16th century men were trying to reach Asia by traveling west from Europe. In order to find Asia they had to find a way past South America. The man who finally found the way from the Atlantic Ocean to the Pacific was Ferdinand Magellan. Magellan sailed from Seville in August, 1519 with five ships and about 280 men. Fourteen months later, after spending the cold winter on the coast of Patagonia, he discovered the channel which is now called Magellan Strait . In November, 1520, after many months of dangers from rocks and storms, the three remaining ships entered the ocean on the other side of South America. They then continued, hoping to reach Asia. But they did not see any land until they reached the islands off the coast of Asia. Before they arrived at these islands, later known as the Philippines, men were dying of starvation. While they were staying in the Philippines, Magellan was killed in a battle. The remaining officers then had to get back to Spain. They decided to sail round Africa. After many difficulties, one ship with eighteen men sailed into Seville three years after leaving. They were all that remained of Magellan's expedition. However, their achievement was great. They were the first men to sail round the world.
Answer: carry men to Philippines
[EX A]:
The purpose of Magellan's expedition was to _ .