back
［误］ I'm sorry. I have to back home.
［正］ I'm sorry. I have to go back home.
［正］ I'm sorry. I have to go home.
［析］ back用作"回到(某处)"之意，不是动词。
be
［误］ Where do you from?
［正］ Where are you from?
［析］ "你从何处来"应为Where are you from?或Where do you come from? 但要注意这两句话均是问对方从哪个国家来的。要是口语中问"你是从什么地方来?"应讲Where did you come from? 回答用I came from the library.
