Select the correct passive form of the given sentence.

The tigress was trailing the stag

The stag was being trailed by the tigress.

The correct passive form of the given sentence is The stag was being trailed by the tigress.

The active voice of the sentence is The tigress was trailing the stag. This sentence is in the simple past tense, which is used to describe an action that happened in the past. The passive voice of the sentence is formed by putting the subject of the active sentence after the verb "to be" and the present participle of the main verb. In this case, the subject of the active sentence is "stag" and the main verb is "trail." The past participle of "trail" is "trailed." So, the passive form of the sentence is The stag was being trailed by the tigress.

The other options are incorrect because:

• The stag had been trailed by the tigress. is in the past perfect tense, which is used to describe an action that happened in the past before another action happened. There is no other action mentioned in the sentence, so the past perfect tense is not appropriate.
• The stag was trailed by the tigress. is in the simple past tense, but the present participle "being" is necessary to show that the action was ongoing.
• The stag was trailing by the tigress. is grammatically incorrect. The verb "to trail" needs to be in the present participle form, which is "trailing."