'Debilitating' means tending to weaken something.
The correct antonym of the given word is option A, 'strengthening' which means to make or become stronger.
Options B, C and D are incorrect because 'enfeebling' means to make weak or feeble, 'occupying' means to fill up space or interesting and 'inhabiting' means (of a person, animal, or group) live in or occupy (a place or environment).