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（1）处应选择（）

A.medium

B.connection

C.token

D.resource

学习活动设计常用的有三种方式，即抛锚式、支架式和（）。

A.协作学习式

B.预告式

C.设计式

D.随机进入式