You work as a network engineer at TestKing.com. TestKing users have noticed extremely slow network performance, intermittent connectivity, and connection loss. After entering the show interfaces command, you notice that the Ethernet interface is configured as 100 Mbps full-duplex and that there is evidence of late collisions. What could be the cause of this problem?（）

A. duplex mismatch
B. a routing loop
C. trunking mode mismatch
D. improperly configured root bridge
E. improperly configured static VLAN