The answer is B: variety in sentence structure and length.
Explanation:
To have good fluency the sentence structure has to vary(so it does not just repeat every time). The length of a sentence must be long enough to make a point, that's why b makes the most since out of all the options.
Top-Down is used to refer to a situation in which decisions are made by a few people in authority rather than by the people who are affected by the decisions
