A friend is a second self.

朋友是另一个自己。

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A friend is a friend; a foe is a foe; one must be clearly distinguished from the other.

敌是敌，友是友，必须分清界限。

《新英汉大辞典》

A friend is an antique dealer in Paris.

我的一个朋友在巴黎做古董商。

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When a friend is troubled by a mistake he has made, you might tell him to forget about it.

VOA: special.2009.05.10

His friend, Remi, is taking him in a limousine to a concert, ] you to think about why that might be important].

他的朋友雷米正要用这辆豪华轿车载他去音乐会，我想留给你们思考这点为什么重要。

耶鲁公开课 - 1945年后的美国小说课程节选

One situation is when you're speaking with a friend who had given you really good advice that you failed to take.

一种情况是，当你正在和一个朋友交谈，他之前曾给你一些很好的建议，但你却没有采纳。

I should have 课堂 - SpeakingMax英语口语达人

Rose: Is is proven that a recommendation from a friend is the best kind?

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You could use it to spot that a friend is a couple of blocks away and arrange an impromptu meeting.

CNN: Face to Facebook: social networks hit the streets

Sharing a pot of tea with a friend is a far more tranquil retreat than a coffee break, even in Boston.

NPR: Tea for You and Me