Ted and Bob are friends. They are both six years old and go to school this autumn.

One afternoon the two boys go by ?a bookstore. Bob looks into the shop window and asks， “Ted， look at these books. Why are some of them so thick， and some of them so thin？”

“What a silly question！” Ted says.

“Is that a silly question？ But I really want to know the answer.”

“Well，” Ted says， “that's because some writers work hard and write a lot， so their books are thick. But some writers are lazy and writes less， so their books are thin.”