Which description is accurate and true of all three sentences?

Question

1. We struggled to understand the complicated algebraic expressions.
2. We could not wait to hear our grades on the final exam.
3. We failed to demonstrate our knowledge and understanding.
A) All sentences have a gerund that takes the place of a verb.
B) All sentences have a participle that replaces a verb phrase.
C) All sentences have an infinitive that takes the place of a noun.
D) All sentences have a participle phrase that functions as an adjective.

Answer 1

And your answer is?

Answer 2

or a

Answer 3

It's one of those two. Do you a gerund when you see it? Do you know an infinitive?

Answer 4

I think it is c.

Answer 5

Yes, they all have infinitives.

Answer 6

It is C I got this question on USA test prep