题目

颜色变化常作为生物实验结果观察的一项重要指标，下面是一些学生在实验中遇到的问题，其中的错误操作或想法有几项（ ） ①用滴管在花生子叶薄片上滴加苏丹Ⅲ染液，发现满视野都呈现橘黄色，于是滴1﹣2滴50%盐酸洗去浮色 ②取新鲜的菠菜叶，加少许SiO2和无水乙醇，研磨液呈黄绿色．于是判断是菠菜叶用量太少导致 ③在纸层析法分离叶绿体中色素的结果中，蓝绿色带最宽，可判断叶绿素a含量最多 ④乳酸菌、酵母菌和蓝藻的细胞内都有核糖体 John is twelve years old. His sister, Mary, is two years younger than he is. One day their mother asked them to clean the house. Because they did a good job, their mother bought a delicious cake and said to John, "John, cut this cake into two pieces, and give one piece to your sister. Don't forget that you must do it like a brother."      "Like a good brother?" John asked. "How dose a good brother do?"      "He always gives the bigger piece to the other person." answered the mother.      "Oh, I see." said John. He thought about this for a short time, and then took the cake to his sister and said to her, "Please cut the cake into two, Mary, and be a good sister." 1. John was ____older than Mary.      A. twelve years         B. ten years              C. two years            D. one year 2. ______ cleaned the house very well.     A. John                  B. Mary                  C. Brother                D. John and .Mary 3. John's mother asked him to give ______of the cake to Mary.     A. the bigger piece                                      B. the smaller piece     C. the better piece                                      D. the thick piece 4. At last John asked _______ to cut that cake.      A. his mother              B. his brother             C. Mary                     D. them 5. In this story there are only ______ people really.    A. two                      B. there                 C. four                        D. five