Billy and Bobby were brothers who often fought with each other.
Last Saturday, their mother said to them, "I'm going to cook lunch now. Go out and play in the garden—and behave yourselves."
"Yes, Mummy," the boys answered and went outside.
They played in the garden for half an hour. Then Billy ran into the kitchen. "Mummy," he said, "Bobby broke a window at Mrs. Allen's house."
"He's a bad boy," his mother said. "How did he break it?"
"I threw a stone at him," Billy answered, "and he quickly ducked."