Who saw the accident...?

[katerina.pata]

Dear teachers,
I think that option A is correct in the following multiple choice
Who saw the accident..........?
a)happen b)happened c)to happen d)to be happening
If so, can you tell me why, please!!!
Thanks a lot. KP

[BobK]

Dear teachers,
I think that option A is correct in the following multiple choice
Who saw the accident..........?
a)happen b)happened c)to happen d)to be happening
If so, can you tell me why, please!!!
Thanks a lot. KP

You are right; but saying why is not so easy. The verb 'see' is followed by a bare infinitive, or by an -ing word (to refer to an action that's continuous); so it could be either "Who saw the accident happen?" or - in the case of a mile-long Canadian-Pacific train being derailed - "Who saw the accident happening". There's not "to" in either case.

b

[katerina.pata]

BobK,
thank you so much for your time!
THANK YOU. KP