— ? — It's terrible.
A:What's he doing
B:How is he?
C:How's it going
D:What's the weather
设i是虚数单位,则复数z=4-3i1-2i的虚部为( )
赫兹用实验证实光是一种电磁波的理论依据有:
①电磁波与光一样都能反生反射、折射____、____和偏振等现象.
②电磁波与光一样都____在真空中传播.
③电磁波与光在真空中的传播速度____.