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Present Perfect VS Present Simple
Как правильно:

Have you seen my dictionary? I need it for my homework
или
Did you see my dictionary? I need it for my homework

I feel terrible today. I think I (have had) или (have) flu.
I (know) или I (have known) Mikhail very well; we are in the same class
We (have had) или (have) very bad luck this year - our car was stolen just before Easter and our flat was robbed a week ago.