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It’s summertime-time once again for mosquitoes to make their appearance. And once they appear, mosquitoes are a total pain. They land on you, bite you, suck out some blood and leave behind an itchy welt（发痒的红肿）.
1 Female mosquitoes must find blood in order to reproduce, so mosquitoes come equipped with finely tuned sensors to help them locate the blood they need.
Mosquitoes’ weapons
Mosquitoes have perfected three different types of sensors. First, mosquitoes can sense several different chemicals. Mosquitoes can smell carbon dioxide and lactic acid（乳酸）up to 100 feet away. 2
Second, mosquitoes have very good eyesight. If you are wearing clothing that contrasts with the background, and if you move while wearing that clothing, mosquitoes can see you. It’s a good bet that anything moving is alive, and therefore full of blood.
Finally, mosquitoes come equipped with temperature sensors, so they can find warm-blood mammals and birds very easily.
3 The female mosquito sticks her proboscis（喙）into you. She sucks about five microliters of your blood into her abdomen.
After she has bitten you, some saliva（唾液）remains in the wound. 4 The area swells and you tich. Eventually, the selling goes away, but the itch remains until your immune cells break down the saliva proteins.
Our defense methods
Because mosquitoes are both a nuisance（讨厌的东西） and a danger, people prefer to stay away from mosquitoes. One way to do that is to use a chemical called DEET, which seems to black a mosquito’s chemical sensors. 5 In some cities there are even trucks that drive around town to spray for mosquitoes. Finally there are to traps. The most popular traps turn propane（丙烷） into carbon dioxide and warmth to attract mosquitoes. Over time, by catching large numbers of mosquitoes, these traps can cause the collapse of the mosquito population in the area.
A．Another way to control mosquitoes is with insecticides（杀虫剂） that kill them.
B．How mosquitoes work is unknown to most of us.
C．Once a mosquito lands on you, it is time to bite.
D．Some bites of mosquitoes are more serious than you thought.E. Mammals and birds give off these gases as part of their normal breathing.
F. The proteins from the saliva create an immune response from your body.
G. But if you ignore the fact that mosquitoes are so annoying they really are amazing.
