This is an instance of dramatic irony, taking into account that this figure of spech is when the implications of a situation, speech, etc, are understood by the audience but not by the characters in the play.
The correct answer is "me".
This words simply means not easily convinced. Or even having doubts.
The word which is so delicate that saying its name breaks it is
SILENCE!!!!
Your answer is A.
This is why:
At the end of this short novel, the audience learns that the Necklace was fake! If Mathilde would have come clean with the fact that she lost it, she wouldn't have had to do all that work and make herself old.