The influenza outbreak in this story began in______.
A. Singapore
B. China
C. Hong Kong
D. India
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The sputniks hanging from the ceiling are intended______.
A. to help maintain (维持) good order in the store
B. to make films that can be used as evidence
C. to be used as evidence against customers
D. to frighten shoplifters by their appearance
A postage stamp's value to collectors is raised if______.
A. there are few others like it
B. there are no errors on the stamp
C. a mistake is made in the printing
D. both A and C
一梁的截面为正方形，若按图示两种方式放置，则两者的刚度关系为()。
A. (a)＜(b)
B. (a)=(b)
C. (a)＞(b)
D. 不能确定
整流滤波电路如图所示，已知U1=30V，及R=2kΩ，稳压管的稳定电流IZmin=5mA与 IZmax=18mA。通过负载和稳压管的电流和通过二极管的平均电流分别是()。
A. 5mA，2.5mA
B. 8mA，8mA
C. 6mA，2.5mA
D. 6mA，4.5mA
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