在正式谈判过程中，双方旁征博引、列举事实、质询与反驳以争取对方让步的阶段称（）
A.妥协阶段
B.交锋阶段
C.协议阶段
D.明示阶段
参考答案：B
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
次生色
