Provavelmente o seu professor segue a linha do inglês americano em vez da linha do inglês britânico. Os americanos costumam a utilizar bem mais o simple past em frases nas quais os britânicos usariam o present perfect (ou seja, em frases nas quais não há referência de tempo passado e até mesmo em frases contendo os advérbios de tempo just, ever, already e yet):
In American English the past simple is often used instead of the present perfect simple, often with already and yet.
Did you eat (yet)?
Did you finish (already)?
Have you eaten (yet)?
Have you finished (already)?
time adverbs with past simple/present perfect
Past-time adverbs, such as just, ever, already and yet are often used with the past simple in American English, whereas in British English they would normally be used with the present perfect. Compare the following:
Did you phone her yet?
Have you phoned her yet?
Did you eat already?
Have you already eaten?
Garry? You missed him. He just left.
Garry? You've missed him. He's just left.
Did you ever go to Canada?
Have you ever been to Canada?
Referências: http://www.bbc.co.uk/worldservice/learn ... v123.shtmlhttp://dictionary.cambridge.org/grammar ... ave-worked