钻机在钻芯过程中应确保不发生倾斜、移位，钻芯孔垂直度偏差不应大于（）。
参考答案：0.5%
— Look! Somebody ________ the sofa.
— Well, it wasn't me. I didn't do it. [ ]
A. is cleaning
B. was cleaning
C. has cleaned
D. had cleaned
周波降低的事故处理。
