单项选择题

Resistance to Malaria 1. "Our job", said the health officer, "is to spray the walls of every house in every town and village in the malaria parts of Mexico". You may be surprised to learn that there are about ninety-nine thousand separate villages and towns. Some are big places like Mexico City, some are single houses deep in the jungles or upon the mountain-tops. The men working with our programme say that most of these localities lie within districts warm enough for the malaria-carrying mosquitoes to live in and spread the disease. That means that we must plan to spray the walls of nearly three million house once or twice a year for five years." 2. "We have studied everything very carefully" , the officer continued. "Our advance guards have drawn maps of some forty thousand parts of the country for use by the spray teams. Each house in the malaria districts has been given a special number. The United Nations has given us cars and trucks to carry the spray teams and their tools, but many of the houses to be sprayed are too difficult to reach by car. Half of our spray teams go on horseback or by boat." 3. "The malaria programme has been popular with the Mexican people. Everyone wants to help. The navy has offered us the services of ships. The Defence Department is helping us plan the movement of men and supplies. The Ministry of Education has printed sheets in Spanish and the more widely spoken Indian languages to explain how malaria is spread and why spraying helps. Doctors have spoken in the churches of many communities to explain the programme." 4. Resistance is a problem. It was in the United States that such resistance to sprays was first proved. Since then many other insects have developed resistance to poisons. Take the case of the housefly and D.D.T. At first D.D.T. killed them off. For a time flies died quickly. Then no more. Now D.D.T. wont hurt a fly. 5. What worries the health workers is the danger that mosquitoes may become resistant. Already resistance to some of the sprays has appeared in parts of the world, although no insect is yet resistant to all of the sprays. A. What worries us B. What we have done C. What’’s our job D. More and more people joined us. E. It will be a hard work. F. What’’s the problem