Fluent classroom questioning combines relevant questions with an appropriate pace.
Why D fits: Asking many meaningful questions within a suitable period can keep students engaged and reveal their understanding.
Why the others are incomplete: Meaningfulness alone does not describe fluency, while a large number of rushed questions may leave no time to think or answer.
Teaching point: Quantity is not the sole goal. Allow wait time, vary the difficulty, invite different students to respond, and use answers to guide the next part of the lesson.