The ground swell of public opinion

I am confused with C option

i also vote for C and sad that answer is A, i thought that it is second best answer
B)had approved is wrong usage, the usage of past perfect implies that senate approved proposals before the ground swell, but the meaning of the sentence says that first it was swell and second approve
C) i don`t see any mistakes, perhaps construction inevitable that is better than inevitable to, may be idiom usage
D)i am not too sure but of the president`s looks like double posessive
we need: proposal of president, or president`s proposal. but we can`t use both of and ` posessive
E) the same as in D

"inevitable of the senate to approve" is wrong and unidiomatic.

Even i chose option C
Correct Answer is option A. Source: Kaplan

The explanation given in the book was something like that the event that is INEVITABLE needs to be in future, so we need to go with option A using the word WOULD

While attempting, I was left with option A and Option C. Probably, the reason i chose option C was because of Placeholder It concept. But re-reading this now, even i feel inevitable of the senate is wrong. We can mark some action as inevitable not any person.

Thanks Sameerballani for the explanation