关于be covered with/by的问题.

题目

关于be covered with/by的问题.
请看例句:
1.Over all,more than 70 per cent of the surface of our planet is covered by water.
2.Most of the earth is covered with water.
为什么一个用by另一个又用with呢?

答案

be covered with是覆盖的意思,表状态.be covered by是被...包裹着的意思 ,表动作.
我是英语教师,再不明可问.