Here are the correct forms of the words in brackets to complete the sentences:

1. Air-conditioning systems have chlorofluorocarbon that is one of the well-known environmental **pollutants**.
2. African and Asian elephant numbers fell dramatically in the 19th and 20th centuries, due to the ivory trade and habitat loss.
**Large**
3. The environmental consequences of large dams are numerous, including direct impacts to the biological, chemical, and **physical** properties of rivers.
4. In areas with high concentrations of tourist activities and attractive natural attractions, **waste disposal** is a serious problem.
5. Unlike pesticides, **fertilizers** are not directly toxic but their presence in fresh water changes the nutrient system.
6. **Erosion** caused by deforestation can also lead to increased flooding.
7. The Earth's natural resources should be consumed at a **sustainable** level.