与粗牙普通螺纹相比，细牙普通螺纹的螺旋升角()，连接的可靠性()。
A．小／高
B．小／低
C．大／高
D．大／低
参考答案：A
You ____ play football in the street. It's too dangerous. [ ]
A. wouldn't
B. needn't
C. mustn't
D. couldn't
______和______是做功的两个不可缺少的因素．
