Answer:
Option A is correct. A bet between two men that one of them can fool society.
Step-by-step explanation:
Eliza was just a flower girl, meaning that she couldn't aspire to anything else in her life. However, after she meets with Higgins who receives a bet from Pickering. After that, the plot continues to center around this fact and has a direct effect even in the ending. Thus, we can say that it is what the plot is centered around!