duty 指按道德和法律的标准，一个人永远要尽的义务，强调自觉性。
obligation 指道义上或法律上对他人的义务，强调强制性。也指因作出承诺而被迫履行的某种义务。
responsibility 指任何义务、职责、责任或职务上所尽的本分，强调对他人的责任。
function 指因职务或职业关系去履行某种职责。
参考例句
1. Is he off or on duty today? （介词）他今天不值班还是值班？
2. Anything subject to duty? 有要报关税的吗？
3. Keeping the classroom clean is our duty. 保持教室清洁是我们的责任。
英英解释
n.
1. work that you are obliged to perform for moral or legal reasons
2. the social force that binds you to the courses of action demanded by that force
3. a government tax on imports or exports
