a piece of cake 可不是“一块蛋糕”的意思，真实意思是“小事一桩、轻而易举的事、小菜一碟、易如反掌的事”。

【例句】
Getting rid of him will be a piece of cake.
摆脱掉他就是小事一桩。

Don't think this job a piece of cake. You'll have to rack your brains once you start on it.
别以为这工作是易如反掌的事，你做了就知道它是很伤脑筋的。