阅读下列短文，把A—E五个句子填入文中空缺处，使短文内容完整正确。
A farmer’s dog, Dolly, had babies, and the farmer needed to sell them. He painted a sign and put it in his yard.      1     , a little boy walked up to him.
“Sir,” he said, “I want to buy one of your dogs.”
“Well,” said the farmer, “these dogs are very expensive.”
“     2     ” asked the boy.
“Sure,” said the farmer. “Here, Dolly!” he called.
Dolly ran out from the doghouse and four little dogs followed her. The boy became excited.
Then, the little boy noticed another dog. This one was smaller.     3     
“I want that one,” the boy said, pointing to the little dog.
The farmer said: “     4      He will never be able to run and play with you like these other dogs.”
The little boy reached down and rolled up one leg of his pants. He showed a cast (石膏) on his leg and a specially made shoe. He said: “You see, sir,       5     , and he will need someone who understands.”