锪圆柱形沉头孔时，应先用直径（）锪钻直径的麻花钻头打孔。
A.大于
B.小于
C.等于
D.近似于
参考答案：B
He didn't pass the exam. He regretted _____ harder. [ ]
A. not having worked
B. having not worked
C. to have not worked
D. not to work
生产性粉尘的理化性质不包括( )。
A．粉尘分散度B．浓度C．比重D．溶解度
