题目

阅读理解 One morning, a little mouse went out to find something to eat. He was careless and met a fierce(凶猛的)lion. The lion caught the mouse. The lion wanted to eat him. “Please let me go, Mr Lion, ”said the mouse. “One day, I will help you. ”The lion laughed, “How could a little mouse help a big lion? ”“Well, ”he said, “I will let you go. But you must walk more carefully. ”The mouse was very thankful. “Thank you, Mr Lion. You are very kind. I will repay(报答)you one day. ”the little mouse said. The next week, the mouse was looking for something to e18．某生物兴趣小组的同学发现夏季多雨天气时落叶很容易腐烂．他们为证明细菌对植物树叶的分解作用，分别提出三种实验方案．其共同之处是：将同一种树的落叶分成甲乙两份．实验过程中滴加蒸馏水，使树叶保持湿润．其他实验条件和步骤如表所示：序号                 实验处理      甲         乙方案一   无菌条件     自然条件方案二先灭菌，再放于无菌条件下     自然条件方案三先灭菌，再放于无菌条件下先灭菌，然后接种细菌，最后置于无菌条件下（1）为什么夏季多雨天气落叶很容易腐烂？细菌的生活需要适宜的温度；（2）该实验的变量是什么？细菌；（3）该实验过程中用自来水代替蒸馏水可以吗？不可以，为什么？因为自来水中含有细菌，对实验结果有影响．（4）你认为哪个实验方案能够达到目的？方案三请说明原因因为方案三除了实验变量外，其他条件都相同．