HY-20G钻机的钻井方式（）
A、空气钻井
B、取芯钻井
C、螺旋钻机
D、顿钻钻井
参考答案：A
It didn't begin to rain _____ I got home yesterday evening. [ ]
A. after
B. until
C. as long as
D. so that
设矩阵。
求矩阵P，使(AP)T(AP)为对角矩阵。
。