已知磷酸分子中的三个氢原子都可与D2O分子中的D原子发生氢交换.又知次磷酸（H3

比一比．谁大谁小？（在横线里填上“＞”“＜”或“=”）

22×4______66

32×3______＞69

243×2______486

132×3______396

112×4______96

33X3______96．

高压管道每一段5m长的管段( )。

A．允许有一个焊接口

B．允许有两个焊接口

C．允许有三个焊接口

D．不允许有焊接口

物料提升机发生如下故障，电压正常，但主交流接触器不吸合。请分析故障发生的可能原因：（）。

A、限位开关未复位

B、相序接错

C、电气元件损坏或线路断开

D、全部正确

导曲线是指道岔中连接（）的曲线轨道。

A、轨翼

B、转辙部分

C、辙叉部分

D、基本轨

Both bus and tree topologies are characterized by the use of multipoint (71) ．For the bus，all stations attach，through appropriate hardware (72) 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 (73) ．A transmission from any station propagates the length of the medium in both directions and can be received by all other (74) ．At each end of the bus is a (75) ，which absorbs any signal，removing it from the bus．

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