The correct option is A acceptable
The adjective form of the verb 'accept' is: acceptable.
Hence, Option A is correct.
'Acceptable' is an adjective that modifies the noun "behaviour".
Option B: 'Acceptance' is the noun form of the word in brackets. Since the question asks for the adjective, this option is wrong. Also, a noun cannot modify another noun 'behaviour'.
Option C: Similarly, 'acceptability' is a noun. Hence C is incorrect.
Option D: The word in brackets is a verb. It refers to an action, whereas the question calls for an adjective. Hence D is incorrect.