单项选择题

蜗杆与蜗轮正确啮合的条件是______

A.mt1=mt2αt1=αt2γ+β=90°
B.ma1=ma2αt1=αt2γ=β
C.ma1=mt2αa1=αt2γ+β=90°
D.ma1=mt2αa1=αt2γ=β