引风机计划停运分为大修、小修和（）三种。
A、定期维护
B、消缺
C、引风机电机试验
D、备用
参考答案：A
3天修完一条路，第一天修了全长的20%，第二天修了800米，第三天修的比前两天的总和少100米，这条路全长多少米？
Her mother is______ . She______ her students now. [ ]
A. a teacher, teach
B. teacher, teaches
C. a teacher, teaching
D. a teacher, is teaching
