Select the correct passive form of the given sentence.

Send these books at my new address.

Let these books be sent at my new address.

The correct passive form of the given sentence is Let these books be sent at my new address.

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 "you" and the main verb is "send." The past participle of "send" is "sent." So, the active form of the sentence is "Send these books at my new address."

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 "these books" and the main verb is "send." The past participle of "send" is "sent." So, the passive form of the sentence is "Let these books be sent at my new address."

The other options are incorrect because:

• These books must be send at my new address is grammatically incorrect. The verb "to must" is followed by an infinitive, but the phrase "must be send" is not an infinitive.
• These books should have been sent at my new address is in the past perfect tense, while the original sentence is in the present tense.
• These books are being sent at my new address is in the present progressive tense, while the original sentence is in the imperative mood.