地球和月球相比，有许多共同属性，如它们都属太阳系星体，都是球形的，都有自转和公转等。

在相同温度和压强下，1体积气体X₂和3体积气体Y₂化合成2体积气体Z，则Z的分子组成为（　　）

A．XY

B．X₃Y

C．XY₃

D．X₂Y₃

磁场中某点的磁感应强度的方向

A．放在该点的通电直导线所受的磁场力的方向

B．放在该点的正检验电荷所受的磁场力的方向

C．放在该点的小磁针静止时N极所指的方向

D．通过该点磁场线的切线方向

水泵轴孔磨损过大，可以用（）方法修复

A、研磨

B、粘接

C、镶套

D、更换

在常见的国产晶闸管中频电源中，逆变器晶闸管大多采用负载谐振式换向方式。

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．tree
B．bus
C．star
D．ring