Step 1: Understanding the requirement
The question asks for a sentence in which:
1. The subject is in the third person plural (they).
2. The verb is in the simple present tense.
Step 2: Analyzing each option
- (A) \emph{Are they here in school now?}
Subject = \emph{they} (third person plural).
Verb = \emph{are} (simple present form of "to be" for plural subject).
This satisfies the condition.
- (B) \emph{They have walked to school.}
Subject = \emph{they} (third person plural).
Verb phrase = \emph{have walked}, which is present perfect tense, not simple present. So this is not correct.
- (C) \emph{Are you not in school yet?}
Subject = \emph{you}, which is second person, not third person plural. Incorrect.
- (D) \emph{He is here in school now.}
Subject = \emph{he}, which is third person singular. Incorrect.
Step 3: Conclusion
Only option (A) has a verb in the simple present tense with a third person plural subject.
\[
\boxed{\text{Correct Answer: (A)}}
\]