on duty 的用法 :the students on duty ___(sweep）the floor when I walked into room

on duty 的用法 :the students on duty ___(sweep）the floor when I walked into room on duty是什么意思及用法 英语翻译rtA method for user-oriented product development hasbeen worked out by the National Swedish Board forTechnical Development (STU) Group on ConsumerTechnology里面的(STU)何解? on duty和on business的用法是?他们前面一定要加be吗? in duty,on duty,off duty,duty free区别The students ________ should clean the classroom.A.in dutyB.on dutyC.off dutyD.dutyl free请问这四个选项的意思 The following people will on duty today. on duty on duty On the whole中on的用法 The police are duty on the duty on road.这里为什么用are 而不是用is? the policeman on duty told him that since his defeat,the ex-Prime Minister had gone abroad.这里since是什么用法呀?如果是自从,这句话貌似不很通顺的 on duty的中文意思是 be on one's duty的意思 I was on duty the next Tuesday.这句话用的是什么时态? the students on duty have clsed the windows改疑问句 struct student{int num,int score}stu; struct student *p;stu *sp和s这两个指针有什么区别,分别有什么不同的用法!请举例说明, Today is my on duty for the day. 英语翻译stamp duty on the level,level怎么解释,