倒换钻具时要求将倒换钻具的长度、钢号、倒换位置和计算结果等详细记录在专用的()记录中,以备查考。
A.钻具丈量
B.钻具计算
C.井深计算
D.钻具变化
参考答案:D
Many rivers ________. [ ]
A. have became polluted
B. have become polluted
C. have been polluting
D. have become polluting
如图所示,沙箱连沙总质量为m1,沙桶连沙质量为m2,如图挂起沙桶,沙箱恰能匀速直线运动,则沙箱与桌面间的动摩擦因数为 ;若将沙箱里质量为△m的沙移入沙桶中,则它们运动的加速度为 .