Final answer:
The correct answer is option d. Cyrano starts when Roxane accuses him of jealousy because he is taken aback by her insight into his secret love for her.
Step-by-step explanation:
Cyrano 'starts', or is startled, when Roxane accuses him of jealousy because it is a reaction to the sudden and accurate insight into his feelings. The best answer to why Cyrano reacts the way he does is D) He is in love with Roxane. Despite his brave and swashbuckling demeanor, Cyrano conceals deep feelings for Roxane; however, he is hindered by his own self-consciousness about his large nose. Cyrano's sensitivity about his appearance and his unrequited love for Roxane are central themes in the play.
Thus, when Roxane accuses him of being jealous, he is taken aback not only because of the unexpected recognition of his feelings but also because it prompts an emotional turmoil regarding his secret love for her.