The correct option is A Sincerity
The word 'adversity' refers to a difficult or unpleasant situation.
Option A, sincerity refers to the absence of pretence, deceit or hypocrisy.
Option B, animosity refers to strong hostility.
Option C, curiosity refers to a strong desire to know or learn something.
Option D, .prosperity refers to the state of being wealthy and affluent.
Thus, according to the meaning, the word 'sincerity' is the opposite of the word 'adversity'.