It sounds like a good idea, but I don't think it will work practically.

　　這個主意聽起來不錯，但我認為它實際上行不通。

　　It sounds like a good idea; let's look at the practicalities and work out the costs.

　　這個主意聽起來不錯。咱們來看看實際運作，計算一下費用。

　　I know it sounds crazy but it just might work.

　　我知道這事聽起來很蠢，然而也許就會奏效。

　　I know it sounds corny, but it really was love at first sight!

　　我知道這聽起來像陳詞濫調(diào)，然而的確是一見鐘情啊！

　　I know it sounds trivial, but I'm worried about it.

　　我知道這事聽起來微不足道，但我還是放心不下。