For more information: A parent can visit nationalzoo.si.edu/events/zoolights.

More ZooLights celebrations: For those outside of the D.C. area, here are some links to other zoos with similar events (not all are free):

Columbus Zoo, Ohio: Through January 1.

Detroit Zoo, Michigan: Through December 31.

Denver Zoo, Colorado: December 2-January 1.

Houston Zoo, Texas: Through January 15.

21. What do we know about the zoo walkways in the National Zoo?

　 A.They are free of charge.

　　B. They light up in time to music.

C. They are usually very crowded all the year round.

　　D. They are very humid in winter.

22. Who are the intended readers of the passage?

　　A. Students. B. Tourists. C. Parents. D. Zoo keepers.

　　Perhaps you think you could easily add to your happiness with more money. Strange as it may seem, if you're unsatisfied, the issue is not a lack of means to meet your desires but a lack of desires----not that you cannot satisfy your tastes but that you don't have enough tastes.

　　Real riches consist of well-developed and hearty capacities to enjoy life. Most people are already swamped with things. They eat, wear, go and talk too much. They live in too big a house with too many rooms, yet their house of life is a hut.

　　Your house of life ought to be a mansion, a royal palace. Every new taste, every additional interest, every fresh enthusiasm adds a room. Here are several rooms your house of life should have.

　　Art should be a desire for you to develop simply because the world is full of beautiful things. If you only understood how to enjoy them and feed your spirit on them, they would make you as happy as to find plenty of ham and eggs when you're hungry.

Literature, classic literature, is a beautiful, richly furnished room where you