已知真空中的电磁波波速是3×108m/s。在真空中波长是5m的无线电波,它的频率是( )
A:6×107Hz
B:1.5×109Hz
C:8×108Hz
D:1.7×108Hz
西周立国,以封建制度为支柱,政治秩序仰赖封建制度来维持。我们对于周代封建的认识,不正确的是( )
- Do you know Victory Day in China?
- Yes, it's _______ September 3rd _______ each year. It tells the world that Chinese people love peace and hate wars. Chinese people will never forget the history.