duty是可數(shù)名詞么

　　duty用作名詞的用法例句

　　I feel it my duty to speak frankly to you.我覺得我有義務(wù)要坦白地對(duì)你說(shuō)。

　　She was ashamed to admit that she hadn't done her duty.她羞愧地承認(rèn)她沒有盡到自己的義務(wù)。

　　He is on night duty three days a week.他一個(gè)星期要上三天夜班。