duty是可数名词么

　　duty用作名词的.用法例句

　　I feel it my duty to speak frankly to you.我觉得我有义务要坦白地对你说。

　　She was ashamed to admit that she hadn't done her duty.她羞愧地承认她没有尽到自己的义务。

　　He is on night duty three days a week.他一个星期要上三天夜班。