know what (you) are doing
to have the necessary knowledge or experience to do something.
Mountain climbing is a dangerous sport, so I hope he knows what he's doing.
英语词组固定搭配大全包含18674条英汉双解词组，基本涵盖了全部常用英文词组、短语的翻译及用法，是英语学习的有利工具。