The correct option is C A stack of CDs had been kept by Aman.
The correct answer is, ‘A stack of CDs had been kept by Aman’. The sentence begins with the receiver of the action ‘a stack of CDs’. It is followed by the helping verb ‘had’, form of the ‘be’ verb ‘been’, the past participle form of the verb ‘keep’, ‘kept’, the preposition ‘by’ and the doer of the action, ‘Aman’.