题目内容：

  A farmer had some dogs to sell. He painted a sign advertising the dogs. A little boy came up to him and said, “Sir, I want to buy a dog.”

“Well,” the farmer said, “but they1.________(be) very expensive.” The boy 2._____(take) some changes(零钱）out of his pocket, “ I’ve got thirty-nine cents. Is that enough to take a dog?”

“Sure. I have six dogs. You3._______(choose) any of them.” Then the farmer whistled, “Dolly!” At once, Dolly ran out of the doghouse followed by four little dogs. Then the little boy’s eyes 4._________(dance) with happiness.

But the boy saw another little dog5.________(move) out slowly. This one was the smallest. She was trying her best6.________(catch) up with the others.“I want that one,” the boy said, 7.__________ (point) to the last one. The farmer was surprised. “She 8._________(not run) and play with you like other dogs. Will you still want to buy her?” he said kindly.

Hearing that, the little boy rolled up one leg of his trousers. A steel brace(支撑物）9.________ (tie) on both sides of his leg. Looking up at the farmer, he said, “ So you see, Sir. I can’t walk very well myself. I10._________(understand) her. So we will be good friends.”