Answer:
c. to cause something to move from the middle
Answer: C. His reputation for clever dealing betrays him when he tells the truth.
The statement in letter c shows irony because it presents contrasting events. Mr. Hauchecorne is a clever person however the irony strikes on him when nobody believes him and makes fun of his cleverness when he said the truth about the string.
The answer seems to be indeed A
Look for sentences that contains synonyms that help you assimilate the worthwhile thing.