单项选择题
A.1:0.3~0.7 B.1:0.4~0.8 C.1:0.5~0.9 D.1:01
A.10~50 B.50~120 C.120~160 D.160~180
A.β=180+2α B.β=180-2α C.α=180+2β D.α=180-2β