Currently, the whole world has been working on how to make the Earth “sustainable.” That means we cannot take what we have now for granted； _21_, we have to reserve what we have now for future generations. For instance, the protection of the rainforests is one of the top _22_ problems today. For one, plants are what keep our air clean. _23_, those plants support all the living creatures that live there. What is more, September 22 is World Car Free Day, _24_ people are encouraged to travel by bicycle, use mass transportation, or walk to any place they need to go to. _25_ more people follow a car-free day, pollution will go down. Therefore, popular awareness of “sustainability” will provide a bright future for humanity and all the other life on Earth.
【題組】21.
(A) better yet
(B) besides
(C) instead
(D) in this way