В предложении "The car was stolen, ... ?" на месте пропуска необходимо поставить конструкцию

The sentence "The car was stolen" is in the passive voice, past tense. To form a question in the past passive, we use the auxiliary verb 'was/were' followed by the subject and the past participle. In this case, 'car' is singular, so we use 'was'. The structure for a question is 'Was + subject + past participle'. Therefore, the correct construction is 'was it'.