半自动闭塞法根据区间线路数分为（）和双线半自动闭塞两种。
参考答案：单线半自动闭塞
_____ to his experiment in the lab, the idea for the new plan came to his mind. [ ]
A. While devoting
B. While devoting himself
C. While he was devoted
D. While devoted
竹茎的节间伸长是（）组织活动的结果。
A.居间分生组织
B.侧生分生组织
C.顶端分生组织
D.成熟组织
