如图所示的三个振动系统中，物块的质量均为m，弹簧的刚性系数均为k，摩擦和弹簧的质量不计。设图(a)、(b)、(c)中的振动频率分别为T1、T2、T3，则有()。
A. T1=T2≠T3
B. T1≠T2=T3
C. T1=T2=T3
D. T1≠T2≠T3
查看答案
纳税人委托其他纳税人代销货物,其增值税纳税义务发生时间为货物移送的当天。()
A. 正确
B. 错误
What did the woman's parents do in Central America？
A. Travel around the area.
B. Volunteer their services.
C. Teach in some schools.
D. Visit relatives in the area.
The tests work most effectively when it is used to measure
A. the whole information on a person.
B. one's creative ability.
C. the skill one has learned.
D. the skill he will learn in the future.
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