COMPUNCTION means the feeling of guilt that prevents or follows the doing of something bad.

The synonym of the word will be a word that has a similar meaning to this word.

REGRET means the feeling of sadness or guilt or disappointment that follows the doing of something bad or wrong. It is a feeling one experiences when someone feels he should not have done what he has done.

Thus the answer is Option A- REGRET.

The remaining options are incorrect because they mean differently:

APPRECIATION means recognizing the worth or value of something or someone.

WONDER means the feeling of awe and amazement.

ANGER means the feeling of vexation and annoyance.