efore 以前,常用语完成时 I have never been there before
ago 之前或多久之前,用于一般过去式 I went there three years ago.
once 曾经 用于一般过去时 I went there once.
ever 在任何时候 ,用于任何时态,完成时较多.Have you ever been there?
efore 以前,常用语完成时 I have never been there before
ago 之前或多久之前,用于一般过去式 I went there three years ago.
once 曾经 用于一般过去时 I went there once.
ever 在任何时候 ,用于任何时态,完成时较多.Have you ever been there?