In the context of the overall argument of the passage, which of the following choices best describes the purpose of the second paragraph? A. It gives a basic definition of REM sleep that is elaborated in later paragraphs.

B. It provides a factual basis necessary to speculate on the subjects babies may dream about.

C. It offers key examples to support the first paragraph’s claim that babies’ brains perform many important tasks.

D. It explains how sleep researchers use alternative sources of evidence to study infant sleep cycles because infants are unable to describe their experiences.

E. It establishes the conventional view about whether babies dream in order to show how the argument of the passage departs from this understanding.