The correct port available for connecting to a SQL database via command-line interface is D. 1521. Port 1521 is the default port for Oracle Database connections using the Oracle Net Services (SQL*Net) protocol. Port 143: This is used for IMAP (Internet Message Access Protocol) communication. Port 445: This is used for Microsoft's SMB (Server Message Block) protocol (file and printer sharing). Port 993: This is used for secure IMAP (IMAPS) communication. Port 1521: This is the default port for Oracle Database connections using the Oracle Net Services (SQL*Net) protocol.