— Why did the dinner party start so late last night?

— It was _____ that caused him to serve dinner an hour later than usual. 

A．we were late

B．we being late

C．our being late

D．because we were late

一个使用普通集线器的10Base-T网络的拓扑结构可描述为（）

A.物理连接是总线型拓扑，逻辑连接是星型拓扑

B.物理连接和逻辑连接都是总线型拓扑

C.物理连接是星型拓扑，逻辑连接是总线型拓扑

D.物理连接和逻辑连接都是星型拓扑