题目

Dr. Yuan was born in Beijing in 1930. 61 he graduated from Southwest Agricultural College in 1953, he has given his life to 62 ( find ) ways to grow more and more rice. As a young man, he saw the great need for increasing the rice output. At that time, famine was 63 serious problem in many parts of the country. Dr. Yuan searched 64 a way to increase rice harvests without expanding the area of fields. In 1950, Chinese farmers could only produce fifty million tons of rice. Last year, 65 , nearly two hundred million tons of rice 66 ( produce ). These increased harvests mean that 22% of the血液中有一种含铜的呈蓝色的蛋白质分子，其相对分子质量约为151 000。已知该分子中铜的质量分数为0.34%，则平均每个蛋白质分子中铜的原子个数为(    ) A.8                     B.6                      C.4                    D.2