A:NO和O2
B:CH4和NH4+
C:N2H4和H2O2
D:HCl和H2O
2009年1月,我国正式进入移动通信的3G时代.移动通信实际上是利用____传递信号的.某手机发射的信号频率是1000MHz,该信号的波长为____m.
Joan was happy because she was given some ____ (use) gifts last week.