[Azar] 현재완료

• 과거의 불명확한 시간에 어떤 일이 일어났을 때 현재완료를 쓴다. 시간이 명확할 때는 단순과거를 쓴다.
  
  They have moved into a new apartment.
  Have you ever visited Mexico?
  I have already seen that movie.
  I have never seen snow.
  
  시간이 명확하면 다음과 같이 단순과거를 쓴다.
  
  I saw that movie last night.
  
  
• 현재 이전에 어떤 행위가 반복적으로 일어났을 때 현재완료를 쓰며, 이 경우에 반복된 사건이 정확히 언제 일어났는가 하는 것은 중요하지 않다.
  
  We have had four tests so far this semester.
  I have written my wife a letter every other day for the last two weeks.
  I have met many people since I came here in June.
  I have flown on an airplane many times.
  
  
  
• 과거에 일어나서 현재까지 지속되는 행위로 for, since와 함께 현재완료를 쓴다.
  
  I have been here since seven o'clock.
  We have been here for two weeks.
  I have had this same pair of shoes for three years.
  I have liked cowboy movies ever since I was a child.
  I have known him for many years.