Which statement about the ip classless router command is true?（）

• A、The ip classless command is enabled by default in recent versions of IOS.
• B、The ip classless command should only be enabled when static routing is being used instead of a routing protocol.
• C、The ip classless command should be enabled by the network administrator whenever RIPv1 or IGRP is being used.
• D、The ip classless command should be enabled by the network administrator whenever OSPF, RIPv2, or EIGRP is being used.