下面哪个不是我国的护照分类之一()。
A.外交护照
B.公务护照
C.普通护照
D.特殊护照
参考答案:D
解析:我国护照分为ABC三类。
一只单摆,在第一个星球表面上的振动周期为T1;在第二个星球表面上的振动周期为T2。若这两个星球的质量之比M1∶M2=4∶1,半径之比R1∶R2=2∶1,则T1∶T2等于
A.1∶1
B.2∶1
C.4∶1
D.2∶1
The radiotelegraph alarm signal is().
A.SOS sent three times
B.ten one-second dashes with a four-second interval between them
C.twelve four-second dashes with a one-second interval between them
D.twelve one-second dashes with a short interval between them