---Tom has been fired by his boss．

---              ? As far as I know, he is a hardworking and considerate fellow．

A．Why not

B．How come

C．What then

D．So what

下列选项中，关于RPR的说法不正确的是( )。

A．RPR是一种在光纤上高效传输IP分组的传输技术
B．RPR采用双环结构，可以实现“自愈环”的功能
C．RPR采用结构与FDDI结构不同
D．采用RPR技术可使宽带的利用率提高