题目

如图所示，两个完全相同的波源在介质中形成的波相叠加而发生的干涉的示意图，实线表示波峰，虚线表示波谷，则（ ） A． A点为振动加强点，经过半个周期，这一点振动减弱B． B点为振动减弱点，经过半个周期，这一点振动加强C． C点为振动加强点，经过半个周期，这一点振动仍加强D． D点为振动减弱点，经过半个周期，这一点振动加强It was a village in India. The people were poor. However, they were not unhappy. After all, their forefathers had lived in the same way for centuries. Then one day. Some visitors from the city arrived. They told the villagers there were some people elsewhere who liked to eat frog’s legs. However, they did not have enough frogs of their own, and so they wanted to buy frogs from other places.This seemed like money for nothing. There were millions of frogs in the fields around, and they were no use to the villagers. All they had to do was catch them. Agreement was reached, and the children were sent into the fields to catch frogs. Every week a truck arrived to collect the catch and hand over the money. For the first time, the people were able to dream of a better future. But the dream didn’t last long.    The change was hardly noticed at first, but it seemed as if the crops were not doing so well. More worrying was that the children fell ill more often, and, there seemed to be more insects around lately.The villagers decided that they couldn’t just wait to see the crops failing and the children getting weak. They would have to use the money earned to buy pesticides(杀虫剂) and medicines. Soon there was no money left.Then the people realized what was happening. It was the frog. They hadn’t been useless. They had been doing an important job---eating insects. Now with so many frogs killed, the insects were increasing more rapidly. They were damaging the crops and spreading diseases.Now, the people are still poor. But in the evenings they sit in the village square and listen to the sounds of insects and frogs. These sounds of the night now have a much deeper meaning1.From paragraph I we learn that the villagers ______.A.worked very hard for centuriesB.dreamed of having a better lifeC.were poor but somewhat contentD.lived a different life from their forefathers2.Why did the villagers agree to sell frogs?A.the frogs were easy moneyB.They needs money to buy medicineC.they wanted to please the visitorsD.the frogs made too much noise3.What might be the cause of the children’s sickness?A.the crops didn’t do wellB.there were too many insectsC.the visits brought in diseasesD.the pesticides were overused4.What can we infer from the last sentence of the text?A.Happiness comes from peaceful life in the countryB.Health is more important than moneyC.The harmony between man and nature is importantD.good old day will never be forgotten