Mosquitoeshaveanextraordinaryabilitytotargethumansfa...

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Mosquitoes have an extraordinary ability to target humans far away and fly straight to their unprotected skin. Regrettably，mosquitoes can do more than cause an itchy(發癢的）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. 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 striking and 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 (斑點).”

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.

28. What do mosquitoes mainly use to find their targets?

A. Sense of smell. B. Sense of touch. C. Sense of sight. D. Smart brains.

29. The first response of the mosquitoes to the objects in the experiment is .

A. to fly to the dark ones

B. to catch and stick to them

C. to take no notice of them

D. to attach themselves to them

30. How can we avoid being attacked by mosquitoes according to the text?

A. Don’t let them see us.

B. Use dark objects to stop them.

C. Make them fly back and forth for hours.

D. Attract them to objects full of carbon dioxide gas.