One should not question _____ does not concern him/her.

Options

A. what
B. that
C. which
D. whatever

Answer

A

Explanation

We use what as a Pronoun to mean the thing(s) that or to ask for information about things and actions.
Look at the sentences :
I can.t decide what to buy Rina for her birthday.
What time are you leaving? Here, what is the right usage.