(it is )my/a pleasure是别人对你进行感谢时的回答语。“这是我/一件很乐意去做的事情”。with pleasure 是别人请你帮忙时的回答语。“非常乐意”如:---Thank you very much.---(it's) my / a pleasure---Could you please do me the favor to pass the book to me?---With pleasure.
treasure