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问题 单项选择题

光纤中波长数及每一波长携带信息量的增加，使光传输容量和速率大为提高、传输成本迅速下降，点对点的光传输系统正在向骨干网或城域网层次的全光网发展。目前，（）bit／s系统已投入商用。

A.320G

B.640G

C.1T

D.2T

答案

参考答案：A

改错题

下列各句中均有一处错误,请找出并改正.

(  )1. That's wasteful to throw away waste paper.

           A          B             C               D

(  )2. Both Tony and Sam has been to the Great Wall.  

          A              B            C   D

(  )3. Everyone in the green school do something to help protect the environment.

                                                       A     B           C         D

(  )4. Those small factories cause too many pollution every day.

                                           A      B      C      D

(  )5. We should do our best to stop the factories from pollute the air.  

                           A                    B                         C     D
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单项选择题

外部正效应指的是（）。

A．社会净收益大于个人净收益，产品产量偏低 

B．社会净收益小于个人净收益，产品产量偏高 

C．社会净收益大于个人净收益，产品产量偏高 

D．社会净收益小于个人净收益，产品产量偏低
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