凡直接从事选煤作业的职工，必须进行（）
A.技术培训
B.安全培训
C.质量培训
D.机电培训
参考答案：A, B
By next summer John _____in this factory for thirteen years.
A．has been working
B．will have been working
C．will be working
D．has worked
下列除杂的操作方法，正确的是
A．NH3中混有少量水蒸气：通过装有浓硫酸的洗气瓶
B．NO中混有少量NO2气体：用水洗涤后再干燥
C．食盐中混有少量NH4Cl：加过量烧碱溶液后加热蒸干
D．硝酸混有少量硫酸：加适量BaCl2后再过滤
