题干

为了研究用基因重组等方法生产的干扰素对癌症的治疗效果,有人计划进行如下实验( )
(1)从癌症患者身上取得癌细胞,并培养此种细胞
(2)给培养中的癌细胞添加干扰素
(3)观察干扰素是否对癌细胞的生长带来了变化
上述的实验计划中存在不足。下列可供选择的改进方法中,正确的是:(    )
①将培养的癌细胞分成两组,一组添加干扰素,一组不添加干扰素,分别观察生长情况
②直接给癌症患者注射干扰素,进行临床实验
③设置一系列不同质量分数的干扰素,分别添加给培养中的癌细胞,观察生长情况

A:②③

B:①②

C:①③

D:①②③

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答案(点此获取答案解析)

C

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    The Marches were a happy family. Poverty, hard work, and even the fact that Father March was away with the Union armies could not down the spirits of Meg, Jo, Beth, Amy, and Marmee, as the March girls called their mother.
    The March sisters tried to be good but had their share of faults. Pretty Meg was often displeased with the schoolchildren she taught; boyish Jo was easy to become angry; golden-haired schoolgirl Amy liked to show up; but Beth, who kept the house, was loving and gentle always.
    The happy days passed and darkness came when a telegram arrived for Mrs. March. “Your husband is very ill,” it said, “come at once.” The girls tried to be brave when their mother left for the front. They waited and prayed. Little Beth got scarlet fever(猩红热)when she was taking care of a sick neighbor. She became very ill but began to recover by the time Marmee was back. When Father came home from the front and at that joyful Christmas dinner they were once more all together.
    Three years later the March girls had grown into young womanhood. Meg became Mrs. Brooke, and after a few family troubles got used to her new state happily. Jo had found pleasure in her literary efforts. Amy had grown into a young lady with a talent for design and an even greater one for society. But Beth had never fully regained her health, and her family watched her with love and anxiety.
    Amy was asked to go and stay in Europe with a relative of the Marches'. Jo went to New York and became successful in her writing and had the satisfaction of seeing her work published there. But at home the bitterest blow was yet to fall. Beth had known for some time that she couldn't live much longer to be with her family, and in the springtime she died.
    News came from Europe that Amy and Laurie, the grandson of a wealthy neighbor, had planned to be married soon. Now Jo became ever more successful in her writing and got married to Professor Bhaer, and soon afterwards founded a school for boys.
    And so the little women had grown up and lived happily with their children, enjoying the harvest of love and goodness that they had devoted all their lives to.