Our professor was perplexed by the answers we wrote in the examination.

Perplexed means completely baffled, very confused, or puzzled. The antonym should convey clarity and understanding. Enlightened means having greater knowledge or understanding, which is the direct opposite of perplexed. Misled means led to a wrong conclusion; confused and befuddled are both synonyms of perplexed. Therefore, enlightened is the correct antonym.