用方框中所给词语的适当形式填空，每词限用一次。

keep  loudly   instead of   natural  sky

It’s not good to talk____ in public places.
As the saying goes, an apple a day____ the doctor away.
Spring is the best time to go out and enjoy the ____ world.
Because of air pollution, it is not always easy to see the blue____ now.
Our English teacher often tells us to do more reading ____ doing exercises only.