小菜一碟
a piece of cake
a piece of cake基本义“一块蛋糕”，引申义“很容易做到的事，小菜一碟”
英语解释为to be very easy。
例
I'm glad to help. It was a piece of cake.
很高兴能帮上忙，这很容易。
Girls were a piece of cake. It was the boy.
女儿还不好对付，让我头疼的是儿子。
Believe me, with your dance background, it'll be a piece of cake.
相信我，以你的舞蹈背景，这是小菜一碟。《老友记》
非常畅销
sell like hot cakes
sell like hot cakes “非常抢手，非常畅销”
英语解释为if things are selling like hot cakes, they are very popular and a lot of people are buying them very quickly。
例
Her latest record is selling like hot cakes.
她的最新唱片非常畅销。
The electrical goods are selling like hot cakes.
这种电子产品很抢手。
鱼和熊掌不可兼得
you can't have your cake and eat it
(1) have your cake and eat it字面意思“既想拥有蛋糕又想吃掉它”，表示“鱼和熊掌兼得”
(2) you can't have your cake and eat it (too)表示“鱼和熊掌不可兼得”
英语解释为you cannot have or do two things that are both desirable but normally contradictory or impossible to have or do simultaneously。
例
Too many people want to have their cake and eat it.
太多人想鱼和熊掌兼得。
You can't have your cake and eat it, too.
鱼和熊掌不可兼得。
