组员小规模交头接耳、自由发挥的技术叫做（）。

A.脑力激荡法

B.耳语聚会

C.菲利普六六讨论法

D.静默法

E.揭示法

If the radio signal ground wave extends out for less distance than the minimum skywave distance，there is an area in which no signal is received．This is called the（）.

A.Skip zone

B.Blackout zone

C.Diffraction zone

D.Shadow zone