Answer:

Introduction:
The correct answer to the question "___________ (you / sleep)?" is "Are you sleeping?". In this answer, we use the present continuous tense to ask someone about their current activity.

Detailed Explanation:

1. Present Continuous Tense:
The present continuous tense is used to describe an action that is happening at the moment of speaking or around the present time. It is formed by using the verb "to be" (am, is, are) followed by the present participle of the main verb.

2. The Verb "Sleep":
In the given question, the verb "sleep" is used to ask about the current activity of the person being addressed. "Sleep" is the base form of the verb, and in the present continuous tense, it becomes "sleeping" when used as the main verb.

3. Subject and Verb Agreement:
The subject of the question is "you," which is the second-person singular or plural pronoun. In the present continuous tense, we use the form "are" with the pronoun "you." Therefore, the correct form of the verb "to be" in this question is "are."

4. Forming the Question:
To form a question using the present continuous tense, we invert the subject and the verb "to be." In this case, the question is asking whether the person is currently sleeping or not. Therefore, we use the question word "are" followed by the subject "you" and the present participle "sleeping."

Conclusion:
In conclusion, the correct answer to the question "___________ (you / sleep)?" is "Are you sleeping?". This answer is formed using the present continuous tense, specifically the second-person singular or plural form "are" with the subject "you" and the present participle "sleeping."