What options may be the besr when a user needs to provide message integrity?

Create a checksum, append it to the message, encrypt the message, then send to recipient.

Th e use of a simple error detecting code, checksum, or frame check sequence is often used along with symmetric key cryptography for message integrity. A is pointless, without sending the message itself to compare hash results. B has a weakness if the attacker ever gets the symmetric key used to encrypt the message. C, while providing privacy, is, by itself, computationally ineffi cient relative to the objective of message integrity. Page 360.