Did he buy a car yesterday? The passive form of the sentence is:

Explanation

The correct answer is Option A: 'Was a car bought by him yesterday?' The original sentence 'Did he buy a car yesterday?' is in the simple past tense. To convert it to passive voice, the object 'a car' is placed at the beginning, followed by the appropriate form of 'to be' in the past tense ('was' for singular nouns), then the past participle of the verb ('bought'), and finally 'by him' to indicate the doer of the action. Options B, C, and D are incorrect as they use different tenses or alter the sentence structure, which changes the intended meaning of the original sentence.