One of the basic relationships in interest rate theory is that, other things held constant, for a given change in the required rate of return, thethe time to maturity, thethe change in price.

b. a single paragraph.

a paragraph is a series of sentences that are organized and make sense, and are all related to a single topic . almost every piece of writing you do that is longer than a few sentences should be organized into paragraphs. this is because paragraphs show a reader where the subdivisions of an essay begin and end, and thus the reader see the organization of the essay into subjects in order to be able to understand its main points.

it's obviously d. it could be c though.