Present perfect

Das present perfect wird gebildet aus dem simple present von have, also:
have/has + past participle
have/has + 3. Verbform (past participle)

I have written/called
he has written/called

Our teacher has just entered the classroom.
We haven't written any tests so far.
Have you had difficulties doing your homework? he asked.

Signalwörter:
since (seit = Zeitpunkt), for (seit = Zeitdauer), until now, up to now, recently, just, this (week, month etc.), all day long, not … yet (noch nicht), so far (bis jetzt), never, ever, already

Die Übung behandelt den richtigen Gebrauch des present perfect in der Gegenüberstellung mit dem simple past.