duty是可數名詞么

　　duty用作名詞的用法例句

　　I feel it my duty to speak frankly to you.我覺得我有義務要坦白地對你說。

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

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