题目

一粒种子长成一棵参天大树的主要原因是(     ) A．细胞数目增多 B．细胞体积增大 C．细胞数目增多、细胞体积增大 D．细胞分裂 答案：CWhen you are home, give a call to let me know you _________safely. A. are arriving　　　 B. have arrived　 C. had arrived　　 D. will arrive