格里菲思和艾弗里所进行的肺炎双球菌的转化实验，证实了（）
①DNA是遗传物质
②RNA是遗传物质
③DNA是主要的遗传物质
④蛋白质不是遗传物质
⑤糖类不是遗传物质
⑥DNA能产生可遗传的变异
A.①④⑤⑥
B.②④⑤⑥
C.②③⑤⑥
D.③④⑤⑥
参考答案：A
解析：格里菲思和艾弗里所进行的肺炎双球菌的转化实验，证明了DNA是转化因子，即DNA是肺炎双球菌的遗传物质；还利用蛋白质和多糖类物质单独与R型菌混合培养，证明了它们不是遗传物质；由于被转化后的R型菌即新的S型菌的后代仍然是S型菌，所以证明了DNA能产生可遗传的变异，A正确。
从下面方框中选择适当的选项填人短文中.选项中有两项是多余的.
The old man entered the restaurant slowly wearing an old coat and trousers. He looked around, but it seemed no one cared __1__ him. A young waitress named Mary saw him __2__ toward a table by the window. She ran over to him, and said, "Here, Sir. Let me give you a hand with that chair. " Without __3__ a word, he smiled and nodded a "thank you". She pulled the chair away from the table. Then she helped him move in front of the chair, and sit __4__ comfortably. In a soft and clear __5__ he said, "Thank you for your kind gestures, Miss. " "You're welcome, Sir," she replied, "My name is Mary. I'll be back in a moment, and if you need anything just wave at me!" After he had finished a meal of cakes and hot lemon tea, Mary brought him the change from his bill. She helped him up from his chair, handed him his coat, and walked with him to the front door. Holding the door open for him, she said, "Come back and see us, Sir!" He turned __6__ and nodded a "thank you". "You are very kind," he said softly. When Mary went to clean his table, she was__7__ to find a business card and a piece of paper under his plate. Under the paper was a one-hundred dollar bill. The paper read. "Dear Mary, I respect you very much, and you respect yourself too. It shows by the way you treat __8__.You have found the secret of __9__. Your kind gestures will shine through to those who meet you. " In fact, the old man was the __10__ of the restaurant where she worked. |