The clever boy made a hole in the wall, ________ he could see what was going on inside the building.

A．on which

B．at which

C．through which

D．in which

在生成树协议（STP）IEEE802.1d中，根据（）来选择根交换机。

A.最小的MAC地址

B.最大的MAC地址

C.最小的交换机ID

D.最大的交换机ID