16．One of the best-known American writers of children's books is Alfred Strong，or Doctor Strong，as he is better known to readers everywhere．Now，an art show called Doctor Strong From Then to Now is traveling around the United States．The pictures and drawings show the history of Doctor Strong．
Doctor Strong first became famous almost fifty years ago when his first children's book was published．Since then，he has written forty-five books that have sold more than one hundred million copies around the world．
Doctor Strong's books are known for their easy use of words and colorful，hand-drawn pictures．These drawings bring life to his imaginary creatures：The Cat in the Hat，Horton the Elephant，The Grinch Who Stole Christmas，and hundreds of others．
The San Diego Museum，in California，organized the art show．It included about three hundred Doctor Strong's original drawings and some of his writings．
Most of Doctor Strong's books，although written in a funny way，have serious messages．For example，in Mc Elligot's Pool，he describes the danger of pollution．He discussed the arms race in The Butter Battle Book，written in 1984．
Doctor Strong is almost eight-four years old now．He says he never planned to write stories just for children．He says he writes sorties that interest people of all ages．He says he used easy words so that everyone，even a child，can understand．
21．Doctor Strong first became famous inD．
A．his eighties when an art show was traveling around the United States
B．his fifties when his drawings and writings were published
C.1984when his book Mc Elligot's Pool was published
D．his thirties when his first book was published
22．Doctor Strong's books are very popular in America becauseB．
A．they are stories about animals such as cats，elephants and so on
B．they are written in easy words with colorful pictures
C．he organized the art show in California
D．they are written in a funny way
23．His purpose in writing many such books isD．
A．to show his original pictures and drawings
B．to organize a social art show of his won
C．to make his readers laugh or smile when they read his books
D．not only to interest people but to expose（uncover） some serious social problems．
