Health officials in Canada are very busy these days. They are placing chickens at fixed points all along their border with the United States of America. That’s a great distance of 2,500km. It’s not a practical joke, nor have the Canadians gone mad. They are using these chickens to see if the deadly West Nile virus is hiding around. The virus infects birds, so they think that the chickens have a good chance of catching the virus, or the virus will catch the chickens. The Canadians are worried because the West Nile virus is transmitted to humans by mosquitoes. It killed seven people in New York last year.
Countries around the world are realizing something important that it may just be possible to stop certain kinds of people from entering their land, but it is very difficult to stop viruses travelling from one end of the earth to the other. When they travel to new places, they sometimes adjust very easily to those climates and start destroying the local plant and animal life. These biological polluters are called smart polluters, which can be carried across borders of countries unknowingly. Just as we humans are travelling across the globe more often than earlier, these biological polluters have also started journeying much more. They travel in the ballast(压舱物）of tankers. They sneak into aircraft through their wheels. They bore their way into objects that air travelers may be carrying from one country to another.
The customs officials in many foreign countries prevent you from bringing in a small plant, or a decorative item made of wood that is in its natural form. They tell you it’s in the rules. They have these rules because they know that these varieties of plants that are special to specific places have the power to spread new diseases among native plants and animals. They always create problems in places where they do not belong. Viruses causing these new diseases could come with special varieties of plants, bugs or even animals.
【小题1】Which of the following best explains “transmitted” underlined in Paragraph 1?
| A．Passed. | B．Supplied. |
| C．Promised. | D．Addressed |
【小题2】Why is it very difficult to stop viruses travelling?
| A．They can hide from anyone. |
| B．They can never be killed in any case. |
| C．They can be spread by many approaches. |
| D．They can evolve to suit any environment. |
【小题3】What can we infer about customs rules from the last paragraph?
| A．Native plants and animals mustn’t be exported. |
| B．Animals can be brought into any country freely. |
| C．No plants can be brought across country borders. |
| D．Special living things are forbidden to be imported. |
【小题4】Which of the following is the best title of the text?
| A．Wipe Out All the Viruses | B．The Smart Polluters |
| C．The Basic Customs Rules | D．A Practical Joke of Canada |
