请问,这句话里怎么有两个动词,一个have to ,一个是is

题目

请问,这句话里怎么有两个动词,一个have to ,一个是is
All we’d have to do to make use of the vast reserves of sea water in the world is to remove the salt.

答案

这是个复合句,并非简单句,具体来说是含定语从句的复合句
All is to remove the salt是复合句的主句部分.
we 'd have to do to make use of the vast reserves of sea water in the world是定语从句
all后面省略关系代词that