单项选择题
For use as protection from gas leaking from a refrigeration unit，each ship must be equipped with a（）.
A.portable ventilation system B.flame safety lamp C.self-contained breathing apparatus D.gas mask
单项选择题 For small，first-degree burns the quickest method to relieve pain is to（）.
单项选择题 Drinking salt water will（）.
单项选择题 Chemical burns are caused by the skin coming in contact with（）.
