题目内容
阅读训练
阅读下面短文,从每小题所给的四个选项中,选出一个最佳答案。
Some of the most beautiful caves are formed in glaciers (冰川).Streams of melting ice and snow tunnel through the glaciers the same way that water from a faucet melts its way through an ice cube. Water from the surface drips down through cracks , hollowing out the tunnels and decorating the caves with crystal icicles (冰柱). The smooth walls and floors are so glasslike that pebbles frozen six feet deep can easily be seen. Crystal-clear icicles draping from the ceilings flash blue green, as though they were carved from precious jewels instead of ice.
Although most of the cave ice in the United States is found in lava caves, there are a number of limestone ice caves as well. Some people believe that this ice was formed thousands of years ago, when temperatures were much colder than they are today. Others think that the cave ice broke off from the ancient glaciers as they spread over the country.
Today many cave scientists have another idea. They believe that cold water sinks down through cracks into these caves until temperature is chilly enough to freeze the water that seeps (渗人) in. The ice that forms keeps the cave cool, and that helps build up still more ice. Many caves become covered with so much ice that no one knows just how thick it is. In some, such as crystal Falls Cave in Idaho, there are frozen rivers and even frozen waterfalls. Native Americans and early settlers used to store food in these underground refrigerators and chip out blocks of ice to melt for drinking water.
1.What is the main idea about this passage?
[ ]
A.Characteristics of glacier.
B.Uses for ice caves.
C.The origin of cave ice.
D.Where glaciers can be found.
2.What causes ice to build up in caves?
[ ]
A.Rivers and waterfalls water.
B.Icicles accumulate on the ceilings.
C.Cave ice breaks off glaciers.
D.Cold water seeps in and freezes.
3.It can be inferred from the passage that the early settlers appreciated the ice caves for their________.
[ ]
A.practicality
B.beautiful interiors
C.historical value
D.precious jewels
4.The author compares icicles to precious jewels based on________.
[ ]
A.appearance
B.cost
C.method of formation
D.availability