Fill in the blanks to complete the sentence:
It is difficult to feel _________ when one is at _________.

The most suitable words to fill the blanks in the given sentence will be "remorseful" and "the top of the world".

Remorseful means feeling deep regret or guilt. At the top of the world means being extremely happy or successful. This would suggest that it's difficult to feel guilty or regretful when one is feeling extremely happy or successful, which makes the most logical sense.

Thus, the correct option is A.