A.m=1 B.1C.m=k D.m>k
A.βA2=10°～20° B.βA2=15°～30° C.βA2=25°～40° D.βA2=30°～60°
A.βA2=15°～20° B.βA2=15°～30° C.βA2=25°～40° D.βA2=30°～60°
