题目

阅读理解 I have an English friend. One day I came to see him. He invited me to dinner. At table, Englishmen had their good manners. To accept a dish was by saying, Yes, please. To decline it was by saying, No, thanks. When eating they made little noise. After dinner he went upstairs to change his clothes. But he didn't come back. After a while I went upstairs and found him in bed asleep. That was his habit. Habits are very strong. If a man by habit saying, thank you and please, it is easy for him to be polite. If a man smokes a great deal, it becomes very difficult for him to s在进行色素的提取与分离实验时，不能让层析液没及滤液细线的原因是(    )A．滤纸条上几种色素会扩散不均匀而影响结果B．滤纸条上滤液细线会变粗而使色素太分散C．色素会溶解在层析液中而使结果不明显D．滤纸条上的几种色素会混合起来