钻架的吊重中心，钻机的卡孔和护进管中心应在同一垂直线上，钻杆中心允许偏差为（）mm。
A.30
B.40
C.50
D.20
参考答案：D
江南经济得以迅速发展，最主要的原因是[ ]
A．气候温暖湿润
B．土地肥沃
C．种植水稻
D．北人南迁
On his 10th birthday, Marty manages to escape from the zoo and gets onto the subway, _____ he believes
that he can go to the wild.[ ]
A. which
B. from what
C. through which
D. that
