Select the correct passive form of the given sentence.

They agreed that the elections should be postponed.

It was agreed by them that the elections should be postponed.

The correct passive form of the given sentence is It was agreed by them that the elections should be postponed.

The sentence "They agreed that the elections should be postponed" is in the active voice. The active voice is formed by putting the subject of the sentence before the verb and the past participle of the main verb. In this case, the subject of the sentence is "they" and the main verb is "agree." The past participle of "agree" is "agreed." So, the active form of the sentence is "They agreed that the elections should be postponed."

The passive voice 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 "they" and the main verb is "agree." The past participle of "agree" is "agreed." So, the passive form of the sentence is It was agreed by them that the elections should be postponed.

The other options are incorrect because:

• It is agreed by them that the elections should be postponed is in the present tense, while the original sentence is in the past tense.
• It has been agreed by them that the elections should be postponed is in the present perfect tense, while the original sentence is in the past tense.
• It had been agreed by them that the elections should be postponed is in the past perfect tense, but it is not the correct passive form of the sentence.