Our house was the oldest in the village. It was nearly three hundred years old. Although we were six children, and a mother and a father, we were not by any means alone in the house. We were sharing it with big families of mice and spiders(蜘蛛). There were great- grandparents, grandparents, fathers and mothers, and hundreds of mouse and spider children. My mother would never let us kill a spider, not even a hairy old grandfather. 'If you want to live and rich,' she used to say, 'let a spider run alive.' And so the spiders, our enemies, were beaten and kicked but never killed. But she had no such dealing with the mice. One of our problems was that my mother hated cats and we never owned a single cat. We kept dogs, often two or three at the same time, but very few dogs can move fast enough to catch a lively young mouse. Every night we set a dozen mousetraps(捕鼠器), each with a small piece of cheese. Sometimes the cheese disappeared, but the mice usually seemed too wise to go near the traps. We seldom caught anything. My mother herself had far better luck. Her arms and hands moved as fast as any cat's paws. Often, when she was scrubbing or polishing a floor on her hands and knees, some foolish little grey fellow would try to run past her. He never got very far. Quick as lightning her hard hands would smack(用掌击) together--and there on the floor would be one dead mouse. 'Oh, you were a proud one,' she would say to it then. One day my father decided to clean out the water tank, which stood on four iron legs in a corner upstairs. He was soon sorry that he had started the job. In the mud at the bottom of the tank, there were sixteen of the little grey fellows, all as solid and hard as stones. We had been drinking the water from that tank for twelve years. Which of followlng statements is true?