1.The missing boy was last seen ____by the lake.答案是playing

问题描述:

1.The missing boy was last seen ____by the lake.答案是playing
2.Betty is often seen _______the old man with his housework.
A.help B.to help C.helped D.helps
答案选的是b
老师的解释是:
当使役动词和感官动词变为被动语态时,不定式就成了主语补语,作主语补语的不定式必须加to.
那为什么第一题不能用to do?
这两题有什么区别?
急.

这是时态的问题,第事实一题是过去正在进行时,第二题是事实常发生的.如果没错就是这样了.