题目

No way! I don’t think         should be allowed to drive．I am worried about your safety．       A.fifteen years old   B.fifteen-year-olds     C．fifteen-year-old 答案：B2．西瓜之所以甘甜可口，主要是因为大量的糖分存在于西瓜果肉细胞的哪一结构内？（　　）A．细胞膜B．细胞核C．液泡D．细胞壁