endangered species: a species of animal or plant that is at risk of extinction

untreated sewage: sewage that has not been processed to remove contaminants

desertification: the process by which land changes into desert, for example because there has been too much farming activity on it or because a lot of trees have been cut down

overfishing: the act of catching too many fish so there are not many left

deforestation: the act or process of removing all or most of the trees from a forest

climate change: long-term changes in Earth's climate, such as rising temperatures and lower rainfall

solid waste: material such as household trash, food waste, yard waste, construction derbis, scrap metal and so on

greenhouse gas: any of the gases that trap the heat in the atmosphere and contribute to global warming

planet: a celestial body distinguished from the fixed stars by having an apparent motion of its own (including the moon and sun), especially with reference to its supposed influence on people and events

country: an area of land that has its own government, army, etc.

alternatives: An alternative plan or method is one that you can use if you do not want to use another one

fossil fuel: a natural fuel, such as coal or oil, formed far underneath the ground and over millions of years from the remains of living things