Scientists at Sus university appear to be on the way to discovering how the mosquito, earner of diseases such as malaria and yellow lever, homes in on its target．The problem is that they have found that the best way to avoid being bitten is: stop breathing, stop sweating, and keep down the temperature of your immediate surroundings．Unfortunately the first suggestion is impossible and the others very difficult.
Scientists have found that there are three distinct stages in a mosquito's assault．Stage one is at fifty feet away, when the insect first smells a man or animal to bite．Stage two is thought to come into operation about twenty-five feet from the target, when the insect becomes guided by the carbon dioxide breathed out by the intended victim．Stage three is when the mosquito is only a matter of inches from its prey: the warmth and moisture given off by the victim is the final clue．The researchers then examined how repellents (驱虫剂) interfere with its three-stage attack．They found repellents act more subtly than by just giving off a nasty smell．A Canadian researcher says that repellents appear to confuse mosquitoes first when it is following the carbon dioxide and second during the find approach, where the warmth and moisture aren't the insect's guide.
Air pervaded by one of the many chemical repellents stops the mosquito reacting to the victim's carbon dioxide, anti the repellent seems to affect the tiny hairs with which the insect senses moisture in the air．The sensors are blocked so that the insect does not know when it is flying through a moist current, or the sensors are made to send the wrong signals.
One positive suggestion from the researchers followed the discovery that mosquitoes on the hunt tend to fly very close to the ground．A dense screen of trees around a village may keep mosquitoes at bay.
The experts also agree that mosquitoes seem to prefer some people to others, but they don't know why.
The phrase 'homes in on its target' (Sentence 1, Para．1) in the context means ______.