Questions 20 to 23 are based on the following passage． White rice is the world ’ s most popular form. of rice. But it goes through a milling process that removes many nutrients（营养成分） . As a result, people who eat a poor diet based on white rice may not get enough vitamin A. Each year about 250, 000 to 500, 000 children go blind from vitamin A deficiency . The World Health Organization（WHO ） says half of them die within a year of losing their sight. Vitamin A deficiency is a problem especially in Africaand Southeast Asia. So scientists thought of an answer. They combined white rice with plant compounds that the body can change intovitamin A. These plant colorings give the rice a golden color. The scientists also thought of a plan to give away this Golden Rice for free to poor farmers. But the rice cannot be madeusing traditional methods. The scientists worked for ten years, until 1990, to develop the technology to add genes to rice. Then it took nine more years to get the genes they wanted into the seed. Professor Ingo Potrykus says rice with two added genes will be available in 2013. One gene comes from maize, or corn,and the other from a soil bacterium （细菌） .Opponents say such crops may cause environmental damage by breeding withother plants. Opponents also question the safety of Golden Rice. However, Mr. Potrykus says Golden Rice has never beenshown to be unsafe for the environment or people. Many agricultural organizations support the project. 20. What is the probable reason why some people do not get enough Vitamin A? A.Because they are short of food B.Because white rice contains no vitamin C.Because they feed on white rice D.Because white rice has no nutrients The underlined word “ deficiency ” in paragraph 2 is closest in meaning to__________ .A.addition B.average C.increase D.shortage When did the scientists begin to develop the technology to add genes to Golden Rice?A.In 1980 B.In 1990 C.In 2000 D.In 2004 What is professor Potrykus ’ s attitude towards the breeding of Golden Rice?A.Doubtful B.Negative C.Neutral D.Positive