About the questions in ACT English

The question is:
Now and then, one member of the audience or another would bend forward _________ intently following an argument that is both complicate and fascinating.

a. as if you were
b. in the posture that is
c. in the position that is

The answer is c. Can you explain why is it?

And also, I had trouble with many idiom problems. The idioms make me crazy and there is no special way to study or so.
Can you guys give some lists of idioms that might be on the ACT English test?

@Marshmallowlove here is some help for Common Two-Part Idioms on the ACT

Not only … but also
Incorrect: Not only did we see the Eiffel Tower, but we saw the Louvre.
Correct: Not only did we see the Eiffel Tower, but also we saw the Louvre.

Between … and
Incorrect: Between cookies or crackers, I like cookies best.
Correct: Between cookies and crackers, I like cookies best.

As … as
Incorrect: Her hair was as pretty than my sister’s.
Correct: Her hair was as pretty as my sister’s.

Either … or/Neither … nor
Incorrect: Neither my best friend or I wanted to go shopping.
Correct: Neither my best friend nor I wanted to go shopping.
If you see one of these in a sentence, check to make sure the other half is present, as well! Keep a list of two-part idioms you encounter in your studies and review them whenever practice!

Idioms with Prepositions
The second way that the ACT will test idioms is when they involve prepositions. A preposition is a word that typically describes location. Many phrases in English are only constructed correctly when used with certain prepositions. These idioms also take recognition and practice to master! Here is a list of some of the most common:
Accused of
Acquainted with
Afraid of
Apologize for
Aware of
Believe in
Capable of
Committed to
Conscious of
Difference between
Encouraged by
Fond of
Guilty of
Hint at
In connection with
Interested in
Limited to
Opposed to
Participate in
Proud of
Similar to
Substitute for
Thank for
Tired of
Worry about
Limited to
Incorrect: Her experience was limited with secretarial work.
Correct: Her experience was limited to secretarial work.

Proud of
Incorrect: I am so proud for my brother!
Correct: I am so proud of my brother!

Afraid of
Incorrect: When I was little, I was afraid from monsters.
Correct: When I was little, I was afraid of monsters.

WOW Thanks for the reply!

Well, you actually typed the question and answer choices wrong.

Real question is this:
Now and then, one member of the audience or another would bend forward _________ intently following an argument that is both complicated and fascinating.

F. as if you were
G. when it was
H. in the posture that is
J. in the position of someone

This is from test 0861D, question 72 in the English section

Answer is J because…

F. Wrong. Includes “you,” which does not match with “one member.” You need another instance of “you” if you want to use “you” again.
G. Wrong. “It” doesn’t seem to refer to anything here. What is “it”? It’s ambiguous, so this choice is wrong.
H. Wrong. This choice sounds like the posture is the thing that is intently following an argument. That makes no logical sense. Only PEOPLE can intently follow an argument. A posture is a position you take, whether literally or figuratively.
J. Correct because it says “of SOMEONE” intently following…
A person can logically follow an argument, so this choice is great.