____ his mother,the baby couldn't help laughing

问题描述:

____ his mother,the baby couldn't help laughing
A.Seeing B.To see
A,why?

A
Seeing his mother,the baby couldn't help laughing.
seeing 是现在分词做伴随状语,表主动.
baby是看到妈妈就笑了,看这个动词是主动的.