Пассивный залог (express the following in the passive) why did they laugh at him

Why did they laugh at him? (Active Voice).

Why was he laughed at by them? (Passive Voice).

In active voice the subject is the doer of the action. In the first sentence the subject is they and they do the action. They laughed at him. The sentence is in past Indefinite.

In passive voice the subject takes the action on it. The second sentence is in passive voice and the subject is he. He was laughed at by them. Passive voice is formed with the help of auxiliary verb to be + the third form of irregular verb or verb + ed when verb is regular.