The twins and I_____agree with each other. A both B all C are all

题目

The twins and I_____agree with each other. A both B all C are all
我认为这道题选C,但是答案是B,这和主语有关系吗?请详细点,谢谢

答案

这句已经有了动词 agree
are属于be动词
一个句子不能有两个动词的啊