A because its asking something about probably the article instead of some that doesn't mean anything
Answer:
b. Cover a single topic.
Explanation:
In any academic writing, or in general any form of writing, it is necessary to make sure that the topical sentence is part of the description of the whole passage. It should and must be the central theme of the work, and must be referred to whenever necessary.
A paragraph can be the distinct and particular section of the work that may or may not discuss the main theme of the whole work. But it is necessary to make sure that a paragraph concentrates on a single topic and not talk of multiple issues/ topics in a single paragraph. Rather, if one point is made in a particular paragraph and another point taken in another paragraph, it will make it easier and more understandable for the readers to get to know the main point of the whole work/ paper.
Because they felt like killing
