Select the correct passive form of the given sentence. The cat ate all the pastries.

All the pastries were eaten by the cat.

The correct passive form of the given sentence is All the pastries were eaten by the cat.

The active voice of the sentence is The cat ate all the pastries. 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 past participle of the main verb. In this case, the subject of the active sentence is "the cat" and the main verb is "eat." The past participle of "eat" is "eaten." So, the passive form of the sentence is All the pastries were eaten by the cat.

The other options are incorrect because:

• All the pastries is eaten by the cat. is grammatically incorrect. The verb "is" is singular, but the subject of the sentence, "pastries," is plural.
• All the pastries are eaten by the cat. is in the present tense, while the original sentence is in the simple past tense.
• All the pastries had been eaten by the cat. is in the past perfect tense, which is used to describe an action that had happened in the past before another action happened. The action of eating all the pastries is not something that had happened before another action happened.