Here are the correct forms for the words in the sentences:

1. Rooftop gardens prevent buildings from absorbing heat from the sun, which can **significantly** reduce cooling bills. **SIGNIFICANT**

2. A great number of environmental campaigns have been carried out all over the world to reduce the **emission** of greenhouse gases. **EMIT**

3. The doctor said I should have the use of sugar **reduction**. **REDUCTION**

4. He widespread **adopted** new information technology that could save $162 billion a year. **ADOPT**

5. If you bring a **sustainable** bag when you go shopping, we can cut down on the number of plastic bags used. **USE**

6. Do you know the oldest type of **sustainable** energy is the biomass that is derived from plant matter? **SUSTAIN**

7. When hiking in the wilderness, it is important to properly **dispose** of anything you can't pack out. **DISPOSABLE**

8. We buy **organic** food at the farmers' market. It costs a little bit more, but we think it's better for our health. **ORGAN**

9. Turning off **electrical** appliances is an easy way to save energy. **ELECTRICITY**

10. Conservation is the protection of things found in nature. **CONSERVE**

11. Avoiding using **harmful** chemicals in farming practices is important for maintaining a healthy and natural ecosystem. **HARM**

12. Recycling **used** materials helps conserve resources and reduce waste in the environment. **USE**