1. Your friend looks worried and upset. You ask:    
What has happened?
What happens?

2. You ask why Fred has a strong accent. Someone tells you:   
He's been living in Australia for ten years.
He lived in Australia for ten years.

3. Fred has cleaned the car. You tell him:   
You didn't have to do that.
You haven't had to do that.

4. You are leaving the party. You tell your host:   
'I have had a wonderful time.'
'I was having a wonderful time.'

5. Miguel's English is suddenly a lot better. You tell him:   
You've been practising!
You practised!

6. Someone asks what you were doing yesterday morning. You reply:   
I've been practising English.
I practised English.

7. Someone asks you how your assignment is going. You say:   
I've finished the research and the first part, now I'm doing the rest.
I finished the research and the first part, now I've been doing the rest.

8. Someone asks if you understand the present perfect. You reply:   
Yes, I've mastered it!
Yes, I master it!