Despite the professor's reputation for _____ and often _____ lectures, his latest seminar was surprisingly _____, prompting several students to rethink their initial impressions.

✓ Correct Answer: Option C

The sentence describes a contrast: the professor's usual reputation for (negative traits) lectures versus a surprisingly (positive trait) latest seminar. 'Arcane' (mysterious, secret), 'recondite' (little known, difficult to understand), and 'pellucid' (lucid, clear) fit this contrast, moving from obscure to clear.