welcome back .welcome是叹词,形容词?动词?

Welcome back to school.句中的Welcome到底是动词还是形容词?back是副词吧,那它修饰Wel Welcome Welcome Welcome back welcome back welcome back, Welcome back! welcome back!是地道的英语么? Welcome 英文翻译,welcome back. Welcome back toschool. welcome back中文 welcome back 怎么读 welcome back to schoo