The Niagara Falls is a popular place for visitors. It is a group of three waterfalls between Canada and the US. They are more than 50 meters high.

The falls freeze in December. People can see thick ice on the top of the falls. It seems that the water does not move. It is not possible. The river is very strong. There is so much water that it can never freeze. Water still runs under the ice.

The falls freeze only once. Ice from Lake Eerie stops the river and it freezes. It cannot happen today. A special steel construction (钢结构) stops the ice. It does not get in the river.

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1.Which is NOT mentioned about the Niagara Falls?

A The location.

B The history.

C The height.

D The visitors.

解析：选B。B细节理解题。根据第一段内容可知，尼亚加拉大瀑布位于加拿大和美国之间，有50多米高，游客很喜欢，并未提及瀑布的历史，故选B。

2.When can people see the falls freeze?

A In November.

B In December.

C In January.

D In February.

解析：选B。B细节理解题。根据第二段第一句The falls freeze in December.可知，该瀑布在十二月会结冰，故选B。

3.Why did the falls freeze?

A Because they were very old.

B Because the ice got in the river.

C Because people stopped the river.

D Because there was no wind in winter.

解析：选B。B 推理判断题。根据最后一段第二句Ice from Lake Eerie stops the river and it freezes.可知，伊利湖的冰阻挡了河流，河就结冰了。由此推断是冰进入了河流导致瀑布冰封，故选B。

4.It is _______ to see thick ice on the top of the falls now.

A easy

B possible

C difficult

D not possible

解析：选D。D细节理解题。根据最后一段It cannot happen today.可知，冰瀑景象今天不可能发生，故选D。