The option that best expresses the given sentence in the Passive Voice is: "The reply must be sent by you."

1. The reply must have been send by you. (Option 2)

   • This uses the past perfect tense "have been sent," which implies the action of sending the reply has already happened in the past, whereas the original sentence refers to a present obligation.

2. The reply must be send by you. (Option 3)

   • This option is grammatically incorrect. The verb "send" should be in the base form after "must be." The correct form is "The reply must be sent by you."

3. The reply must have been sent by you. (Option 4)

   Similar to the first option, this uses the past perfect tense and doesn't accurately reflect the ongoing requirement to send the reply.