Explain why it is so. (тема урока The Present Perfect Tense) ...

Motes

Explain why it is so. (тема урока The Present Perfect Tense)
Объясни следующее. 
Example: - There are no pies on the plate. John (eat).- John has eaten them.1) - Their house is now yellow!- Yes, they (paint) ... .2) - He knows everything about Moscow.- I think he does. He (be) ... there many times.3) - John, your car looks so clean!It should be! I (wash) ... .4) - Your grandparents are tired.Yes, they (come) back from the shops.5) - Does Harry know about it?- Yes, I (give) ... him a call.6) - Is the book interesting?- I don't know yet. I just (begin) ... reading it.7) - Why is Jason in hospital?- He (fall) ... off his bike.8) - Roy knows nothing about our meeting.- Sorry. I (not, speak) ... to him yet.