The phrase “bright side” in this context refers to the positive or favorable aspects of a situation. Therefore, the option that best conveys the meaning of the underlined portion in the sentence is “cheerful”.

Being an optimist, our professor always sees the cheerful side of most things.

This implies that the professor, due to his optimistic nature, tends to focus on the positive, uplifting, or hopeful aspects of situations.

The other options do not fit as well in this context:

• “Charming” (Option A), “illumined” (Option B), “brilliant” (Option C), and “pleasing” (Option D) could all potentially describe positive aspects, but they don’t capture the specific connotation of optimism and positivity implied by the phrase “bright side”.