Answer:
B.
The topic sentence outlines (obviously) the topic of an essay or other written work. This usually contains the main idea (think about an introductory paragraph. A topic sentence is this, but condensed into a sentence.)
What is the underline phrase the question is referring to?
a distinct section of a piece of writing, usually dealing with a single theme and indicated by a new line, indentation, or numbering.
This is a declarative sentence! =)