It took people three months to build this great building.
A:two hundreds
B:hundred of
C:hundreds of
D:two hundred of
把一段带叶的茎下端插入装有稀释红墨水的瓶子里,放置在温暖的阳光下,待到叶脉微红时,用肉眼观察茎的横切面,染红的结构是
共有____个