— Can you come on Saturday or Sunday?

— I'm afraid _____ day is possible.[ ]

A. none

B. either

C. some

D. neither

广播电台和电视台都是利用电磁波来传递信号的．电磁波在空气中传播速度约为______m/s．无线电波属于电磁波，光______（选填：“属于”或“不属于”）电磁波．