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
查看答案
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
某反应的速率方程为：v=kcA2·cB，若使密闭的反应容积减小一半，则反应速率为原来速率的()。
A. 1/6
B. 1/8
C. 1/4
D. 8倍
微信支付 
支付宝支付