I'm at a loss for words，用来表达不知说什么好，无话可说，哑口无言。
例句：
I'm at a loss for words , How dare you accuse me of stealing .
我真不知道该说什么好，你怎么会怀疑是我偷窃呢。
This is the most wonderful gift I've ever received , I'm at a loss for words.
这是我收到的最棒的礼物，我都不知道该说什么好了。
Gosh, that girl is dad gorgeous ,I'm at a loss for words.
天哪，那女孩太美了，我都无法形容了。