Sure! Here are the rewritten sentences:

1. **He was sick, so his father asked him to stay at home.**
2. **There was an accident, so I was late.**
3. **She failed the University entrance exam due to her poor grades.**
4. **My wife insists on buying the Tivi because of its cheap price.**
5. **We still went to school despite the heavy rain.**
6. **I passed the exam because I studied hard.**
7. **Hoa was rich, so she could buy that house.**
8. **His father requested him to stay home because he was sick.**
9. **Due to her poor grades, she failed the University entrance exam.**
10. **I was late because there was an accident.**
11. **I couldn’t go to school because the rain was so heavy.**
12. **She failed her University entrance exam because of her bad grades.**

Let me know if you need anything else!