The correct answer is B. It conveys the subject of the paragraph.
Explanation:
A paragraph is usually composed by a topic sentence and a set of supporting details, in the case of the topic sentence, this is a phrase or sentence that is usually the first sentence in the paragraph and that expresses what the paragraph is about, this means in the topic sentence the main idea of the paragraph is set. In the case, of the supporting details, these are the other sentences of the paragraph that explain the main idea or the idea expressed in the topic sentence. Thus, a good topic sentence is a sentence that expresses or conveys the subject of the paragraph or what the paragraph is about.
The result part of the sentence is then written in the "would + infinitive verb" form; this is called the present conditional tense. For example: I would answer if he called. If the weather improved, our crops would flourish.
