A:did
B:was doing
C:has done
D:had done
—When is National Day?
—_________.
工厂中,贾师傅每天生产10个零件,李师傅每天生产20零件,现需要300个零件,若贾师傅和李师傅合作生产,x天可完成任务,列出等量关系式为____