Multiple choice. Please give a brief explanation for your answer.

When a user needs to provide message authenticity, in the absence of a secure channel, what options may be the best? A) Send a digital signature of the message to the recipient B) Encrypt the message with a symmetric algorithm and send it C) Create a checksum, append it to the message, encrypt the message, then send it to the recipient D) Encrypt the message with a private key so the recipient can decrypt with the corresponding public key