现场通常是以钻井的转盘补心（）平面为标准来计算油层位置和下井工具位置的。
A、上
B、下
C、中间
D、水
参考答案：A
I_____ violin lessons every two weeks, but I think I'll make it every week from next month.[ ]
A. am having
B. have had
C. have
D. have been having
28+372+153+47=（28+372）+（153+47）使用了[ ]
A．加法交换律
B．加法结合律
C．加法交换律和结合律
