現在完成式(Prsent Perfect)

1. 過去到現在的經驗
   *  Have you ever been to Japan? 
   *  Have you been to Japan before?

2. 是否已完成
   * Have you eaten dinner yet? 
   * Have you already eaten dinner?

3. 從過去到現在都還是
   * How long have you been a student?