know something from something
phrasal verb with know verb uk/nəʊ/ us/noʊ/ knew | known
辨别;识别
to know the difference between two things and therefore be able to recognize either, used especially to mean that you have a good knowledge and understanding of a particular subject
Computer expert? He doesn't know a mouse from a modem! (= He knows nothing about computers.) 电脑专家？他连鼠标和调制解调器都分不清！