— What do you think of the little girl's singing on the Walk of Fame, a program on CCTV?

— _____and everybody present was____. [ ]

A. Impressing; impressed

B. Impressed; impressive

C. Impressive; impressed

D. Impressive; impressing

假设电磁波在空气中以光速传播，则传播过程中(    )

A．频率减小

B．周期变大

C．波长变小

D．振幅减小