Although their new factory building is still under          construction, we have already placed        order for 200 pairs of shoes.

A．the; an

B．a; an

C．/; an

D．/; /

把一段带叶的枝条下端插入装有稀释的红墨水的瓶子里，放置在温暖的阳光下，待到叶脉微红时，观察茎的横切面，染红的结构是 [ ]

A．韧皮部的导管

B．木质部的导管　　

C．韧皮部的筛管

D．木质部的筛管