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问题 选择题

向氢氧化钙的饱和溶液中加入下列物质，不可能使溶液的pH 有明显改变的是：  [ ]

A. 通入CO2      

B. 加入稀H2SO4   

C. 加入盐酸      

D. 加入Na2CO3溶液

答案

答案：D

单项选择题

热爱邮政事业，忠于本职工作是邮政职业道德中（）的要求。

A、尽责

B、守纪

C、尽职

D、创优
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单项选择题

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．tree

B．bus

C．star

D．ring
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