The correct answer is: The letter has already been sent. It must have reached by now.
The verb “send” is transitive, which means it requires a direct object. In this case, the direct object is “the letter.” The past participle of “send” is “sent.” Therefore, the correct sentence is “The letter has already been sent.”
The other options are incorrect because they are not in the past participle form. The verb “send” is conjugated as follows:
- Present tense: I send, you send, he/she/it sends, we send, you send, they send
- Past tense: I sent, you sent, he/she/it sent, we sent, you sent, they sent
- Past participle: sent
The past participle is used to form the perfect tenses, which are used to express actions that have been completed or that happened before a certain point in time. In this case, the perfect tense is used to express the fact that the letter has already been sent.