In the following question, a sentence has been given in Active/Passive voice. Out of four alternatives suggested, select the one, which best expresses the same sentence in Passive/Active voice.Who ate the last pastry?

The given sentence is in the Active Voice and Simple Past Tense ($V_2$ form: "ate").The structure for changing an interrogative sentence starting with "Who" in the Simple Past into Passive Voice is:
$$\text{By whom + was/were + object + }{V}_3\text{?}$$
Alternatively, it can be framed as:
$$\text{Object + was/were + }{V}_3\text{ + by whom?}$$
Active: Who (Subject) ate (Verb) the last pastry (Object)?Passive: The last pastry (Object) was eaten (was + $V_3$) by whom?Option A perfectly captures this grammatical rule.