19 is A , 18. Is C. 21. Is A
Ecology gives all species including us; food, water, shelter, and so on.The smallest difference can set everything off balance. A good example would be global warming. You would think that 2 degrees every decade would be a small change, but nothing in ecology is small. Plants need a certain temperature to thrive, if that temperature changes they die. A certain animal may be dependent on that plant for food and when that plant dies so does that animal. Another animal may also be dependent on that other animal for food, and with that animal gone it will also die. It's a viscous cycle that holds lots of power on us humans.
(I hope that helps)
