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 travelling 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(出版). Since then, he has written forty-five books that have been 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 early drawings and some of his writings.
　　Most of Doctor Strong's books, although written in a funny way, have serious messages. For example, in McElligot's Pool, he describes the danger of pollution. He discusses the arms race(军备竞赛) in The Butter Battle Book, written in nineteen eighty-four.
　　Doctor Strong is almost eighty-four years old now. He says he never planned to write stories just for children. He says he writes stories that interest people of all ages. He says he uses easy words so that everyone, even a child, can understand.
Doctor Strong first became famous in _______.

A．his eighties when an art show was travelling around the United States

B．his fifties when his drawings and writings were published

C．nineteen eighty-four when his book McElligot's Pool was published

D．his thirties when his first book was published

Doctor Strong's books are very popular in America because _______.

A．they are stories about animals such as cats, elephants and so on

B．they are written in easy words with colourful pictures

C．he organized the art show in California

D．they are written in a funny way

His purpose in writing many such books is_______.

A．to show his early pictures and drawings

B．to organize a special art show of his own

C．to make his readers laugh or smile when they read his books.

D．not only to interest people but to show some serious social problems up