使用酸性洗剂时，作业人员应戴好胶手套、口罩，注意安全。
参考答案：对
轻比重和重比重溶液的比重是相对于（）
A.注射用水
B.生理盐水
C.脑脊液
D.乙醇
E.空气
---He was almost killed once.
---When was ______?
---______ was in 2012 when he was in the college.
A．that; It
B．this; This
C．this; It
D．that; This
