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 statements is the CORRECT inference from the above passage?

The correct answer is: To do well in an exam, adequate sleep must be part of the preparation.

Step-by-Step Explanation:

1. Analyze the Given Passage:
- The passage states that students often overlook the importance of sleep during exam preparation.
- Research shows that sleep deprivation significantly reduces the ability to recall learned material.
- Therefore, sacrificing sleep to study for extra hours can backfire (be counterproductive).

2. Evaluate the Options based on Logical Inference:
- Option 1: "Sleeping well alone is enough to prepare for an exam. Studying has lesser benefit."
Incorrect. The passage emphasizes that sleep helps retain learned material, but it does not state that sleeping alone can replace studying.

- Option 2: "Students are efficient and are not wrong in thinking that sleep is a waste of time"
Incorrect. The passage explicitly argues the opposite—that cutting down on sleep is counterproductive, meaning students are incorrect in ignoring the value of sleep.

- Option 3: "If a student is extremely well prepared for an exam, he needs little or no sleep."
Incorrect. The text mentions that sleep deprivation reduces recall capability regardless of preparation. Hence, sleep remains essential.

- Option 4: "To do well in an exam, adequate sleep must be part of the preparation."
Correct. Since memory retention depends on adequate sleep and cutting sleep hinders performance, adequate sleep is a necessary component of effective exam preparation.