题目

一条根不断生长是因为（ ） A . 根冠不断更新细胞，分生区也不断地增加新细胞 B . 成熟区细胞不断分裂产生新细胞 C . 伸长区细胞不断伸长，成熟区形成大量的根毛 D . 分生区细胞不断分裂，伸长区细胞迅速伸长 答案：D He said he ________ me a present unless I ________ in doing the experiment． [　　] A． had not given; had not succeeded B． would not give; succeeded C． will not give; succeed D． would not give; will succeed