With the weather getting hot, bites caused by mosquitoes not only annoy people, but can result in many infectious diseases. Even when people wear long clothes, mosquitoes' complex biting mechanism enables them to bite some of them through.
  It would be great if clothing could be used to completely prevent people from getting bitten. Researchers tested graphene（石墨烯）， a material that is incredibly thin but really strong, in order to find out if it can make clothing resistant to mosquitoes.
  In the lab experiment, volunteers exposed a small patch of skin on their arm or hand to roughly 100 mosquitoes for five minutes at a time. Researchers tested three different situations： volunteers wearing no protection, wearing cheesecloth（薄纱棉布）， or wearing cheesecloth plus a thin graphene layer under it.
  A video camera was then used to record and quantify mosquitoes' behavior, including whether they landed on the skin, how long they stayed there, and whether they began to draw blood. The number of bites each volunteer got was also calculated based on how many swellings developed on their skin afterward. Finally,researchers dropped a little water or sweat on top of the graphene layer and studied the consequence, and they also tested a slightly different graphene layer called "reduced graphene".
  As a result, the number of mosquito bites on naked skin was the highest, about 16 on average； skin only protected by cheesecloth got the second, approximately 10 per five minutes' exposure. The exciting finding was that there was no swelling developing on skin covered by the thin graphene layer under cheesecloth,which means the material is effective at preventing mosquito bites. The mosquitoes landed on skin totally uncovered or covered in cheesecloth about 23 times on average,and stayed for one to two minutes. Comparatively, the mosquitoes landed on skin covered in the graphene layer fewer than 10 times, and the length of their stay was much shorter. Besides, water or sweat can ruin the graphene layer, which allows mosquitoes to bite through it. But fortunately, the number of mosquito bites in either dry or wet conditions can be lowered as long as the graphene material is improved to a certain extent.



Why did researchers conduct the experiment？ ______

A. To record the behavior of mosquitoes.
B. To find a substance to prevent mosquito bites.
C. To find a solution to stop infectious diseases.
D. To test graphene's effectiveness in preventing mosquito bites.

What does the underlined word "draw" in Pargaraph 4 probably mean？ ______

A. bleed
B. lose
C. test
D. suck

In which way did researchers draw a conclusion？ ______

A. By analyzing the reasons.
B. By comparing the statistics.
C. By classifying three situations.
D. By recording mosquitoes' behavior.

Which of the following shows how the text is developed？ ______

A. Cause-effect.
B. Opinion-fact.
C. Assumption-conclusion.
D. Phenomenon-evaluation.