75. SMTP (Simple Mail Transfer Protocol) is a purely ASCII text-based protocol, which implies it can only transfer ASCII texts. However, most users often attach multimedia files, which are definitely not text files, in their emails. Which is the correct description about the email attachment？ (A) Because the attachment file can be encoded into texts and therefore it can be delivered though SMTP. (B) Because SMTP is a legacy protocol and is extended to a new protocol called IMAP (Internet Message Access Protocol), which supports binary file attachment and is widely used nowadays. (C) Because most email clients will create additional side channels to the email receivers. That is, the attached files are delivered though different channels. (D) None of the above.