英语翻译Every object has weight.But the center of its weight is

英语翻译
Every object has weight.But the center of its weight is not always in the middle of the object.If the top of an object is heavier than its bottom,it will fall over easily.We say that its center of gravity 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 in the bottom of this box.It will not fall,because its center of gravity is above its bottom.
71．If the bottom of an object is its top,it will fall over easily.
A．lighter than B．heavier than C．no heavier than D．as heavy as
72．Please point out which box will not fall.
73．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
74．If an object has a low center of gravity,.
A．it won’t fall B．it won’t fall easily
C．it is sure to fall over D．its top must be heavier
75．The main idea of the passage is .
A．why things fall over B．a low center of gravity
C．a high center of gravity D．that everything has weight