精确等级为7级的蜗杆传动的接触斑点沿齿高方向应不少于（）
A.60%
B.55%
C.50%
D.45%
参考答案：A
142. Let's meet at the school at nine to morrow morning, shall we?.
A．gate
B．door
C．playground
D．Ground
设int x=7,则～x的值是( )。
A) -8 B) -7 C) -1 D) 1
