单项选择题 The standard protocol used for sending Internet e-mail is called ( ). It works in conjunction with POP servers.

单项选择题 To download a file from a remote FTP server, you can ( ).the command promptB、type 'ftp' in brower's address columnC、click on the FTP icon to see if the client is presentD、All above

多项选择题 成为商业秘密的条件是（）。‌