Here are the combined sentences using "IF":

1. If we recycle, we’ll save natural resources.
2. If you are careful, you won’t fall over the rocks.
3. If you work too much, it can make you feel tired.
4. If you are not careless, you won’t break the vase.
5. If she wants to pass the exam, she has to work hard.
6. If he buys recycled products, he can do his part to save the environment.
7. If we put garbage into the bins, it is one answer to minimize pollution.