Which statement best describes an expository text?
a. it provides a first-person account of a personal experience.
b. it presents information using a common structure.
c. the primary purpose is to construct a logical argument.
d. the author's feelings are more prominent than are facts.

b.It presents information using a common structure.

Expository writing, which is informative by nature, will always contain certain elements, and these elements are characteristic of how an expository piece is organized (or structured).  All expository writing will contain a main idea, support, then a conclusion.  And, this organization (or structure) is, again, common to all types of expository writing.

The statement that best describes am expository text is answer B

presents information   using a common structure

quite an interesting way to teach topic sentences, because the answer to this question is the best definition of a topic sentence that one can present, it is as if answering the questions taught you how to do it, this is some real teaching, it is terribly well-done.

the topic sentence in this paragraph is:

topic sentences writers stay on track and keep a paragraph from becoming an aimless collection of sentences about an idea.

which incidentally tells you what a topic sentence should be.