题目

阅读短文，从每题所给选项中选出可以填入空白处的最佳选项。Johnnie Martin was born in a worker's family. His parentslived a simple life, saving money for the day when they could send him to agood university. They had dreamed that their son could get a good1and live a better life. However, to Johnnie, school lessons seemedlike a wall that was hard to go through. One day when he was in Grade 11, Johnnie went2school psychologist's office to ask for help.Johnnie, I've been studying your marks of all thetests at school. I've made a3 study of them, said the psychologist.I've我们吃不同的水果，会有不同的味道，如甜的、酸的或苦涩的，这主要是因为细胞质中存在（     ）导致的。 A叶绿体    B线粒体    C液泡    D中心体