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). A transmission from any station propagates the length of the medium in both directions and can be received by all other (4). At each end of the bus is a (5) , which absorbs any signal, removing it from the bus.

空白（4）处应选择（）

A:routers B:stations C:servers D:switches

Wind, wave and tides all suffer from the fact that they are variable sources of power output. For example, there will be times when due to windless days or calm seas—and both can occur for periods of several days even in the winter time—they are producing little or no power.
Insofar as this shortfall has to be made up by electricity from conventional power stations, these newer energy sources would not necessarily reduce the installed capacity of such conventional stations needed to meet the total demand on windless or calm days. What the newer sources will do is to save fuel that would otherwise be burned in conventional power stations.
Pumped storage reservoirs could in principle be used to counter this effect, but there 1 is not enough additional reservoir capacity available. We therefore face the same type of storage problem as in solar energy. Thus, unless some new method of energy storage can be developed or we move to the widespread use of a fuel like hydrogen, the wind and wave schemes will be at an economic disadvantage.

Alternative sources of energy （）

A:could not possibly reduce the installed capacity of conventional power stations B:might not reduce the installed capacity of conventional power stations C:would automatically reduce the installed capacity of conventional power stations D:would make it necessary to reduce the installed capacity of conventional power stations

Both bus and tree topologies are characterized by the use of multipoint (16) ．For the bus，all stations attach，through appropriate hardware (17) 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 (18) ．A transmission from any station propagates the length of the medium in both directions and can be received by all other (19) ．At each end of the bus is a (20) ，which absorbs any signal，removing it from the bus．

A:routers B:stations C:servers D:switches

Both bus and tree topologies are characterized by the use of multipoint（）．For the bus，all stations attach，through appropriate hardware（）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（）．A transmission from any station propagates the length of the medium in both directions and can be received by all other（）．At each end of the bus is a（），which absorbs any signal，removing it from the bus．

A transmission from any station propagates the length of the medium in both directions and can be received by all other（）．

A:routers B:stations C:servers D:switches

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（4）处应选择（）

A:routers B:stations C:servers D:switches

Both bus and tree topologies are characterized by the use of multipoint（）．For the bus，all stations attach，through appropriate hardware（）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（）．A transmission from any station propagates the length of the medium in both directions and can be received by all other（）．At each end of the bus is a（），which absorbs any signal，removing it from the bus．

A transmission from any station propagates the length of the medium in both directions and can be received by all other（）．

A:routers B:stations C:servers D:switches

Both bus and tree topologies are characterized by the use of multipoint （） . For the bus, all stations attach, through appropriate hardware （） 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 fromthe （） . A transmission from any station propagates the length of the medium in both directions and can be received by all other （） . At each end of the bus is a （） , which absorbs any signal, removing it from the bus.

A transmission from any station propagates the length of the medium in both directions and can be received by all other （）.

A:routers B:stations C:servers D:switches