A.γ=0°、α=40°、β=50° B.γ=50°、α=40°、β=0° C.γ=0°、α=50°、β=40° D.γ=50°、α=0°、β=40°
A.20 B.30 C.40 D.50
A.60° B.45° C.30° D.90°