题型:阅读理解 题类:常考题 难易度:普通
Mosquitoes have an extraordinary ability to find humans far away and fly straight to their skin. Mosquitoes can do more than cause an itchy (发痒的)wound. Some mosquitoes spread several serious diseases, including Dengue, yellow fever and malaria.
Over one million people worldwide die from these diseases each year. New research now shows how mosquitoes choose who to bite.
Mosquitoes need blood to survive. They are attracted to human skin and breath. They smell the carbon dioxide gas, which all mammals breathe out. This gas is the main way for mosquitoes to know that a warm-blooded creature is nearby.
But mosquitoes also use their eyes and sense of touch. Michael Dickinson is a professor at the California Institute of Technology. His research shows how these small insects, with even smaller brains, use three senses to find a blood meal.
Michael Dickinson's team used plumes—a material that rises into the air of carbon dioxide gas into a wind tunnel (隧道). They then used cameras to record the mosquitoes. The insects followed the plume.
Then, the scientists placed dark objects on the lighter colored floor and walls of the tunnel. Mr. Dickinson said, at first, the mosquitoes showed no interest in the objects at all. “What was quite surprising is that the mosquitoes fly back and forth for hours. These are hungry females and they completely ignore the objects on the floor and wall of the tunnel. But the moment they get a hit of CO₂, they change their behavior quite obviously and now would become attracted to these little visual blobs (斑点).”
This suggested to the researchers that a mosquito's sense of smell is more important in the search for food. Once mosquitoes catch a smell of a human or animal, they also follow visual signals.
Arriving in New York There are three airports in New York. When you arrive at one of them, you can take a bus or a taxi to any place in New York. |
Eating out There are many kinds of food in New York. And you shouldn't eat at McDonald's every day. There are good restaurants in Little Italy and Chinatown, for example. |
Hotels There are lots of good hotels in New York. The best is the Plaza on the 5th Avenue(大街), but you don't have to spend a lot in the city, there are lots of smaller hotels. The YMCA near the Central Park is great for young people. |
Public Transport(交通) In New York, there's a good bus and subway(地铁)service. If you are planning to use the subway a lot, you should buy a subway ticket for the journey because it's cheaper. But you don't have to use the public transport, there are lots of places you can go to on foot, such as the Empire State Building, the 5th Avenue and the Central Park. The New Taxis are a part of the city experience, so you should take at least one taxi during your visit! |
Places to see Finally, there are a lot of places to see in New York—the Times Square, the Statue of Liberty, and so on. And you shouldn't go home without climbing the Statue of Liberty to enjoy the scenery of the city. |
Shopping Shopping in New York is fun. There are big shops on the 5th Avenue. They are seven days a week. But be careful when you look at the prices; you have to pay a special 8% tax(税)on everything you buy in New York. |
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