每个钻杆两端都有螺纹（）螺纹上在钻杆两端。
A、细牙内
B、粗牙内
C、细牙外
D、粗牙外
参考答案：A
To improve the quality of our products, we asked for suggestions _____ had used the products. [ ]
A. whoever
B. who
C. whichever
D. which
在状态检修中，预警的分类有（）。
A.状态量预警
B.部件预警
C.设备类型预警
D.以上都是
