Pollution is always a good way to go but you don't have to do air pollution you can do water pollution or both air and water pollution.
The answer would most likely be D. Mass Extinction
The answer is Energy cannot be created nor destroyed.
The circulatory system is made up of blood vessels that carry blood away from and towards the heart. Arteries carry blood away from the heart and veins carry blood back to the heart. The circulatory system carries oxygen, nutrients, and hormones to cells, and removes waste products, like carbon dioxide.
