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.”