percent特指百分比，proportion指比例
例句
1、
The proportion of single parent families varies between different income groups.
单亲家庭比例在不同收入群中各不相同。
2、
The proportion of small cars on America's roads is increasing.
美国公路上小汽车的比例在逐渐增加。
3、
Water covers a large proportion of the earth's surface.
水覆盖了地球表面的大部分。
