【正确答案】Since 1949, Chinese agricultural scientists have bred many kinds of crops, including many high-yield and good-quality new varieties with strong resistance. Thus the major crops have been updated four to five times, with an increase of the yield by 10 to 30 percent each time. The per-hectare yield of grain crops in China has increased from 1.16 tons in 1950 to 5.62 tons. Meanwhile, agricultural departments have imported more than 100000 crops and seedlings from the rest of the world and have cultivated new varieties of rice, corn, wheat and other crops. Many new advanced technologies, which have played an important role in promoting the farmers’ sci-tech education, have found their extensive application in agricultural production.