电、气焊工作结束，还应做好哪些工作方可离开工作现场？
参考答案：必须切断电源、气源，检查现场，确认无起火危险后方可离去。
25. So carefully _____ the boy ______ his homework ______ he was praised.
A．does, finish, that
B．did, finish, than
C．had, finished, when
D．did, finish, that
什么叫“工业管道”和“公用管道”？
