问题：

[单选] Which statement is true about the components of a queuing mechanism？（）

A . Each subinterface has its own hardware queue and can experience congestion just like its main interface
B . Hardware queuing is only used if the software queues are experiencing congestion.
C . Hardware queues and software queues are not used concurrently.
D . The hardware queuing system always uses the FIFO queuing mechanism.