In one sentence explain why carbon dioxide is considered the most important greenhouse gas, although it traps much less heat than other greenhouse gases such as methane, nitrous oxide and CFCs.

Because plants need carbon dioxide more than any other compound/element. Also, heat doesn't make much of a difference in a plants growth or production. It's sunlight that makes a difference.

trachea, alveoli, lung capillaries, arteries

b is the correct answer