张茜升入初中后，很注意自己在老师和同学心目中的形象，她的衣服总是干干净净，和男女

When I try to understand ______ that prevents so many Americans from being as happy as one might expect,

it seemed to me that there are two causes. [      ]

A. why it does

B. what it does

C. what it is

D. why it is

中药天花粉指的是葫芦科植物（）的块根。

婚姻发展形式？

慢性肾功能不全的分期是

A．肾功能不全代偿期，尿毒症期

B．肾功能不全代偿期，氮质血症期，尿毒症期

C．肾功能不全代偿期，失代偿期，肾功能衰竭

D．尿毒症早期，尿毒症晚期

E．肾功能不全失代偿期，尿毒症期

排列图中累计百分数为（）%是C类因素。

A.100

B.90～100

C.80

D.10