1. Although he earn a small salary, he is happy
-> In spite of his small salary, he is happy.
2. She doesn't have enough money so she can't buy the dictionary.
-> If she had enough money, she could buy the dictionary.
3. We visited our old school when we went to Ho Chi Minh city.
-> We haven't visited our old school since we went to Ho Chi Minh City
4.Hoa can't go to school because she is sick. -
> Hoa is sick, so she can't go to school.