We should have _____ sense of responsibility to do something to help _____ poor whenever they are in

_____ trouble. [ ]

A. a; 不填; the

B. a; the ;不填

C. 不填; the; the

D. a; the; the

在焊接环境中可能存在的化学有害因素有电焊烟尘及（）等。

A、电焊弧光

B、有毒气体

C、高频电磁场

D、热辐射