1. Andy and I have known each other since we met in a summer camp four years ago.
2. The children have been watching TV for 2 hours.
3. How long have you been learning to play the piano? When did you begin?
4. Peter is phoning just now. He says he was buying food at 5 o'clock yesterday.
5. I see that your hat is wet. Have you been swimming?
6. Would you like a piece of cake? I have just made it.