Which of the Following Is a True Statement Regarding SMTP

Which of the following is a true statement regarding SMTP processing of messages?

A) Messages typically are sent through multiple SMTP systems while going from the sender to the recipient.
B) The SMTP sender remains responsible for a message until it has been delivered to the recipient.
C) SMTP does not guarantee that all messages are delivered.
D) SMTP attempts to send messages until the recipients become available.
E) SMTP allows only one recipient for each message that is sent.