在多个电源共同作用的 电路中，各支路的响应均可看成是由各个独立源单独作用下、在该支路上所产生响应的 ，称为叠加定理。
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6. Every means __________ tried but without much result.
A. has been
B. have been
C. are
D. is
下列属于人际交往的规则的是()。
A. 熟悉效应
B. 邻近效应
C. 相似规则
D. 个人特质
7. There _________ in this room.
A. are too much furniture
B. is too many furnitures
C. are too much furnitures
D. is too much furniture
8. Not only I but also David and Iris __________ fond of playing basketball.
A. am
B. is
C. are
D. was
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