正常人在安静、清醒、闭目状态时，所记录的脑电图主要是( )

A．α波

B．β波

C．δ波

D．θ波

E．α和β波

In areas covered by Inmarsat HF can be used as an（）to satellite communications.

A.alternation

B.alternate

C.alter

D.alternative