下列哪种储存方式可以长时间保存蛋白质(    )
   A．溶液状态常温保存
   B．溶液状态4℃保存
   C．硫酸铵溶液中以沉淀方式4℃保存
   D．硫酸铵沉淀蛋白，离心后在液氮中保存
   E．冻干的粉末形式保存

A．People were not very interested in the new stamps.
B．The new stamps are believed to be the most popular stamps in British history.
C．People just went to the post offices to have a look.
D．People formed long lines to see Princess of Wales.

A.通过与阴离子去垢剂作用后，蛋白质获得负电荷，使得所有蛋白质带的电荷相等

B.依据蛋白质分子的净电荷或等电点进行分离的技术

C.利用两性电解质可以在电场中形成正极为酸性，负极为碱性的连续pH梯度

D.电泳迁移率与等电点有关