在气路中设置了（）bar的安全阀，以防压力开关失效。
A.6.0
B.7.5
C.9.0
D.10
参考答案：D
It is believed that ________ December 21st, 1891, the first basketball game in history was played.
A．on
B．in
C．at
D．by
在进给量和背吃刀量选定以后，（）增大，切屑易折断
