有关拓展性课程《校园植物观察》活动过程中，某同学制作了植物分类检索表如下，请你与该同学一起分析下列问题：

1a 植物无花，无种子，以孢子繁殖···························································2

1b 植物有花，以种子繁殖······································································3

2a 小形绿色植物，结构简单，仅有茎、叶之分···········································A

2b 通常为中形或大形草本，很少为木本植物，分化为根、茎、叶···················B

3a 胚珠裸露，不包于子房内···································································C

3b 胚珠包于子房内···············································································D