The correct sentence is: “The police asked the lady to take off her mask to check her identity.”
- “Take off” is a phrasal verb meaning to remove clothing or accessories.
- “Take over” means to assume control — not suitable here.
- “Take of” is grammatically incorrect (missing extra 'f').
- “Take across” means to transport something — unrelated to the context.
Thus, the only correct and meaningful choice is (C) take off.