Why is the answer 'assisted' but not 'rendered'?

Question

Qn - None of the onlookers ________ any aid to the injured man after he was attacked by two men on the street.

a) helped
b) assisted (means in doing something to help)
c) rendered (means to give help)
d) supported

Answer 1

It isn't. Rendered is correct. You can't assist aid, though you can assist a person.

Another possiblity is "offered."

Answer 2

I also say it is rendered. Why do you think it is assisted. It could be a typo or other mistake.