题目内容：

    A population of the world's most aggressive mosquito species was almost completely wiped out by an experiment on two islands in the southern Chinese province of Guangdong, according to a study published.

The experiment successfully reduced the female Asian Tiger Mosquito population — the main source of bites and disease spread — by up to 94%, reducing the number of reported human bites by 97%.

One of the Chinese study's researchers, Xi Zhiyong, a professor at Michigan State University, has been a longtime pioneer in this field of study. Running a mosquito factory in southern China, he previously attempted to use sterilized male mosquitoes to mate with unaltered females which developed normally. In the new study, published by the International Journal of Science, Xi and his colleagues attempted to cut mosquito numbers even further by limiting both males and females' ability to reproduce. The results were so successful that they nearly killed the entire female mosquito population on the two islands.

It isn't the first attempt by researchers to reduce mosquito populations across the world. In 2018, scientists from the Imperial College of London used gene-editing tools to make female mosquitoes sterile, while males developed normally and continued spreading the genetic mutation (突变).Experts said the Asian Tiger Mosquitoes are particularly hard to kill using traditional population control methods, such as pesticides (杀虫剂) and removing stagnant (不流动的) water where the insects lay their eggs.

Mosquitoes create grave threats to human health beyond just bites. The World Health Organization (WHO) has described the insects as "one of the deadliest animals in the world," due to their ability to rapidly spread deadly diseases such as dengue fever and malaria. There is currently no effective vaccine or treatment for most mosquito-spread diseases, leaving controlling the insects' populations one of the most effective control methods, according to the International Journal of Science. “A new tool like what's being described in this paper is very much needed” said Stephen Dobson, a professor of medical insectology at University of Kentucky.

1.What does the underlined word "unaltered" in paragraph 3 refer to?

A.Unchanged. B.Undivided.

C.Unadopted. D.Unfinished.

2.Why do mosquito populations have to be controlled?

A.Mosquitoes cause genetic changes in humans.

B.Mosquitoes spread some deadliest diseases.

C.Mosquitoes limit people's ability to reproduce.

D.Mosquitoes make traditional vaccines ineffective.

3.What has been the most successful way of reducing mosquito numbers?

A.Editing genes in female mosquitoes.

B.Sterilizing male mosquitoes before mating.

C.Limiting both genders' reproduction ability.

D.Using pesticides and removing stagnant water.

4.What can we learn from Stephen Dobson's words?

A.The things described in this paper are not practical.

B.A better way of mosquito control is yet to be found.

C.Xi Zhiyong' s method has proven to be very effective.

D.A new tool is needed in order to improve Xi's research.