粗径钻具上端带反丝钻头是为了防止（）等卡钻。
参考答案：地层错动、缩径、掉块和探头石
—Do you know the famous singer Wang Lihong came to Nantong on May 19?
— Yes. _____ he appeared on the stage, all the audience couldn’t help clapping.
A．If
B．As soon as
C．Unless
D．Before
依据工艺性质不同冷冲模具可分为（）
A.冲裁模
B.弯曲模
C.拉延模
D.冷挤模
