正常成年人一定体积的血液中细胞数目最多的是___________，血液中有凝血功能的是__________。
红细胞 血小板
All possible means ____, but nothing can prevent the buildings ____. [ ]
A. has tried; from being pulled down
B. have tried; from pulling down
C. has been tried; from pulling down
D. have been tried; from being pulled down
三角形形态的形成要求至少确立（）转折点。
A.3个
B.4个
C.5个
D.6个
