Stumped [stʌmpt]
把某人难住

不知道怎么解决问题/如何做某事
不知怎么回答某个问题/感到迷惑

Question 42 has me a stumped. I don't know what the answer could be.
42题把我难住了。我不知道答案会是什么。

We've been stumped all day on how to do the client's new marketing campaign.
如何进行客户新一轮的市场营销难了我们一整天。

Don't have a clue
毫无头绪

have no idea

I don't have a clue on what you want me to do. You say you want me to come over then you say you hate me.
我对于你想让我做什么毫无头绪。你让我来，然后又说你恨我。

We have no clue how this could happened.
我们也不确定这事儿怎么就发生了。

I have no idea how this could happened.
我完全不明白这事怎么发生的。

At a loss
很迷茫/不确定

We are at a loss for how this could have happened. There's no explanation.
我们也不确定这事儿怎么就发生了。一个解释都没有。

At a loss for words
太惊讶以致于不知道说什么

have no words

So you're telling me she has a dog and a cat in her apartment, but at the same time she says she hates animals. I'm at a loss for words.
所以你是说她家里有一猫一狗，但同时她又说她讨厌动物。我无语了。

Left speechless
无语，惊呆

She left the room speechless when she punched Gary in the mouth.
当她对着Gary的嘴打完一拳之后，屋里人都惊呆了。