PrepTest C - Section 3 - Question 08

I am confused as to why the answer is A and not C.

In the conclusion:

"But this cannot be so, for unless some uses of words are literal, there can be no nonliteral uses of any words."

is the first part:

"for unless some uses of words are literal"

a part of the premise?

Admin Note: Edited title. For LR questions, please use the format: "PT#.S#.Q# - brief description of the question."