What a pity! I _____ in London for three more days, but something urgent needed to be dealt with back in Beijing.

A．must have stayed

B．could have stayed

C．may have stayed

D．needn’t have stayed

对10Mbps网络上任意两个节点之间，不能超过（）中继器，或共享集线器。

A.2个

B.4个

C.5个

D.1个