The importance of sleep is often overlooked by students when they are preparing for exams. Research has consistently shown that sleep deprivation greatly reduces the ability to recall the material learnt. Hence, cutting down on sleep to study longer hours can be counterproductive.Which one of the following statement is the CORRECT inference from the above passage?

• A. To do well in an exam, adequate sleep must be part of the preparation.
• B. If a student is externally well prepared for an exam, he needs little or no sleep.
• C. Students are efficient and are not wrong in thinking that sleep is a waste of time.
• D. Sleeping well alone is enough to prepare for an exam. Studying has lesser benefit.