Gary and Gavin were twin brothers who worked in a department store owned by their father. After their father had passed away, they took over the store. Everything went well until the day a twenty-dollar bill disappeared. Gary had left the bill on the cash register. But when he returned, the money was gone. Gary then asked his brother Gavin, "Did you see that twenty-dollar bill on the cash register?" Gavin said that he had not. But Gary did not let it go and kept questioning. "Twenty-dollar bills can't get up and walk away by themselves! Surely you must have seen it." There was accusation in Gary's voice. Tempers began to rise and anger grew. "I said I didn't see it!" Gavin raised his voice. The quarrel divided the young men and they could no longer work together. Later, a wall was built in the center of the store. For twenty years, they never said a word to each other. One day, a strange man came to the store. He walked in and asked Gary, "How long have you been here?" Gary replied that he'd been there all his life. "Then you are the person I'm looking for, since I must tell you the truth," the customer said emotionally. "Twenty years ago, I was totally _ and hungry. I entered this store from the back door and saw a twenty-dollar bill on the cash register. And I took it. All these years I hadn't been able to forget that. I had to come back and ask for your forgiveness ." The stranger felt very surprised when seeing tears come to the eyes of the middle-aged man in front of him. "Would you please go next door and tell the same story to the man in the store?" Gary asked. Then something surprised the stranger even more --- after hearing his story, the two middle-aged men hugged each other and cried together in the front of the wall of the store. After twenty years, the wall of anger that set them apart finally came down. The writer wanted to tell us at the end of the story that   _  .
the wall in the center of the store fell down by itself. the stranger pulled down the wall in the center of the store. the twin brothers pulled down the wall in the center of the store. the twin brothers didn't hate each other any longer.