问题
单项选择题
Both bus and tree topologies are characterized by the use of multipoint(1)．For the bus,all stations attach,through appropriate hardware(2) known as a tap,directly to a linear transmission medium, or bus. Full-duplex operation between the station and the tap allows data to be transmitted onto the bus and received from the(3).Atransmission from any station propagates the length of the medium in both directions and can be received by all other(4).At each end ofthe bus is a(5),which absorbs any signal, removing it from the bus．
空白（3）处应选择（）
A.tree
B.bus
C.star
D.ring
答案
参考答案：B
解析：
总线型和树型拓扑都使用多点传输介质。对于总线来说，所有的站都是通过称为接头的专用硬件直接连接到线性传输介质--总线上。站与接头之间的全双工操作使得既可以向总线上发送数据，又可以从总线上接收数据。任何站发送的数据都向总线两端传播，可以被所有站接收。在总线的两头各有一个终接器，它吸收并从总线上移去所有的信号。