A blue whale can be more than thirty metres long and weighs over 150 tons.为什么要加be?

题目

A blue whale can be more than thirty metres long and weighs over 150 tons.为什么要加be?

答案

can 是情态动词,后面要加动词原形.如果这句话不加情态动词,应该是：
A blue whale is more than thirty metres long and weighs over 150 tons.
is 的原形是be,所以can+be