Ravi impressed everyone with his persuasive and fluent speech.

The correct answer is C. Eloquence.

Eloquence is the quality of being persuasive and fluent in speech. It is often used to describe someone who is able to speak in a way that is both clear and persuasive. Ravi impressed everyone with his persuasive and fluent speech, so he is likely to be considered an eloquent speaker.

The other options are not as accurate descriptions of Ravi’s speech. Discourse is a general term for any kind of spoken or written communication. Expression is the act of showing or describing something in words or actions. Lecture is a formal talk or speech, especially one given to a group of students or other learners.