Final answer:
The Warden is trying to find a legal guardian for Zero.
Step-by-step explanation:
The Warden repeatedly asks Mr. Pendanski if Zero had any family or social worker who might have taken an interest in him because the Warden is trying to find a legal guardian for Zero.
Option D is the correct answer. The Warden is responsible for the well-being of the boys at the detention center, and in the absence of family or a social worker, the Warden wants to ensure that Zero has a legal guardian to look after him.
By asking about potential witnesses or people who might have taken an interest in Zero, the Warden is exploring the possibility of finding a suitable legal guardian who can provide care and support for Zero after his time at the detention center.