Jawaban:

1. I have bought a new car since I work at the bank.
2. My sister has started a new job since August.
3. She has already submitted her paper since last Monday.
4. We have been to Singapore since last Tuesday.
5. Peter has gone to the bookstore for two hours.
6. There has been an accident near here.
7. My father has broken his leg since he was 40.
8. My students have improved their English since I taught them.
9. They have had a newborn baby for two weeks.
10. My friends and I have worked hard for last three years.