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The correct answer is B.

OBJ-1.5: To securely upload a file, the employees could use SFTP (Secure FTP) or SCP (Secure Copy). Both SFTP and SCP operate over port 22, therefore port 22 must be opened by the firewall so that the employees can reach the file servers. Port 21 is used by the File Transfer Protocol, but it is not a secure method of sending files. There is a more secure version of FTP known as FTPS, but that uses port 990. Port 25 is reserved for the simple mail transfer protocol (SMTP), which is an internet standard communication protocol for electronic mail transmission. Port 161 is reserved for simple network management protocol (SNMP), which is a networking protocol used for the management and monitoring of network-connected devices in Internet Protocol networks.

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