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【单选题】Some pessimistic experts feel that the automobile is bound to fall into disuse. They see a day in the not-mo-distant future when all autos will be abandoned and allowed to rust. Other authorities, how...
A.
keep in the right lane
B.
wait to arrive at his destination
C.
keep in constant touch with the computer center
D.
inform the system of his destination by phone
【单选题】Some pessimistic experts feel that the automobile is bound to fall into disuse. They see a day in the not-too-distant future when all autos will be abandoned and allowed to rust. Other authorities, ho...
A.
How to render automobiles pollution-free.
B.
How to make smaller and safer automobiles.
C.
How to solve the problem of traffic jams.
D.
How to develop an automated subway system.
【单选题】如图所示的电路可将声音信号转化为电信号，该电路中右侧固定不动的金属板b，与能在声波驱动下沿水平方向振动的镀有金属层的振动膜a通过导线与恒定电源两极相接，若声源s沿水平方向做有规律的振动，则（ ）
A.
a振动过程中，ab板间的电场强度不变
B.
a振动过程中，ab板所带电量不变
C.
a振动过程中，灵敏电流计中始终有方向不变的电流
D.
a向右的位移最大时，ab两板所构成的电容器的电容量最大
