Английский. Объяснить употребление времён.

Vera: Hello, Mike! What are you doing here?
Mike: Hello, Vera! I am reading for my mathematics exam.
V.: But your group has passed it already, hasn't it?
M.: Yes, it has, but I was absent at this time. So I'll take this exam tomorrow.
V.: Is it difficult for you to take this exam?
M.: No, it is not. I have finished a specialized mathematical school where mathematics was studied more thoroughly (тщательно) than at other schools. Besides, I have taken part in a mathemat-ics contest of our city.
V.: Really? Have you? When was it?
M.: It was last year.
V.: Were you the first at this contest?
M.: No, I was the second. The first one was the boy from one of the
Novosibirsk mathematical schools.
V.: Have you ever been to Novosibirsk?
M.: Yes, I have been there this year with a group of students of our
faculty.
V.: What have you seen there?
M.: Oh, I have seen a lot. But now I have no time to tell you about
it. Well, Vera, what are you doing here? Are you reading for
your exams too?
V.: No, I am not. I've passed all my exams with good marks this
term and so my holidays have already started. I'm waiting for
my friend here. Good luck, Mike.