The suggested answer is B.
The cable type most likely connected to an expansion card that allows a computer to receive faxes over a VoIP line is CAT3. This type of cable is traditionally used for telephony and would be compatible with standard telephone systems, which aligns with the need to receive faxes. CAT6, although more advanced, is typically used for higher-speed networking and not specifically suited for telephonic connections required for fax over VoIP.