在证明DNA是遗传物质的几个著名经典实验中，在实验设计思路中最关键的是（）
A.要用同位素标记DNA和蛋白质
B.要区分DNA和蛋白质，单独地、直接的观察它们的作用
C.要分离DNA和蛋白质
D.要得到噬菌体和肺炎双球菌
参考答案：B
解析：证明DNA时遗传物质的实验有肺炎双球菌的转化实验和噬菌体侵染细菌实验，它们取得成功的关键是想办法将DNA与其他物质分开，单独地、直接地观察它们的作用，故B正确。
| 短文填空。用方框中的词的正确形式填空，将短文补充完整(注意大小写)。 | |
I'm not 1_____, I have too many rules in my house, I have to get 2_____ at six o'clock every morning. I can't meet my 3_____ after school because I have to do 4_____ homework. I can't watch TV on school nights. And I have to be in bed by ten o'clock. 5_____ weekends, I have to 6_____ my room and wash my clothes. Then I 7_____ to help my mom make 8_____. Later I have to go to 9_____ Children's Palace to learn piano. I never have any fun. What 10_____ I do? Zhao Pei |