Question

Every object has weight．But the center of its weight is not always in the middle of the object．If the top of ail object is heavier than its bottom (底部)，it will fall over easily．We say that its center of gravity (重力) is high．But if the bottom is heavier, it won’t fall easily, Then we say that its center of gravity is low．

Look at the first picture．This empty box must fall over, because its center of gravity (C) is not above the line of its bottom (AB)．

Now look at the second picture．There is some heavy iron (铁) in the bottom of this box．It will not fall，because its center of gravity is above its bottom．

1.If the bottom of an object is         its top，it will fall over easily．

A．1ighter than                     B．heavier than

C．no heavier than                  D．as heavy as

2.Please point out which box will not fall．

3.The reason why the Leaning Tower of Pisa does not fall is that         ．

A．the top of the tower is heavier than its bottom

B．the bottom of the tower is not heavier than its top

C．its center of gravity is still above the line of its bottom

D．its center of gravity is not above the line of its bottom

Answer

1.A

2.C

3.C

【解析】

试题分析：短文大意：每个物体都有重量。但其重心并不总是在物体的中间。如果上面所有对象比其底部较重，它会轻易摔倒。我们说，它的重心高。但如果底部较重，它不会很容易摔倒，我们就说它的重心很低。

1.A细节理解题。根据第一段中If the top of ail object is heavier than its bottom (底部)，it will fall over easily．可知如果上面所有对象比其底部较重，它会轻易摔倒。所以该选A。

2.C细节理解题。根据第三段Now look at the second picture．There is some heavy iron (铁) in the bottom of this box．It will not fall，because its center of gravity is above its bottom．的描述可知该选C，因为它的重心在底部。

3.第一段末But if the bottom is heavier, it won’t fall easily, Then we say that its center of gravity is low．可知比萨斜塔不会倒是因为它的重心没有高过底部，所以该选C。

考点：科普类阅读。