关于二维凝胶电泳的双向电泳以下捕述正确的是(    )
   A．第一向以蛋白质电荷差为基础，第二向以蛋白质分子量差异为基础
   B．第一向以蛋白质分子量差异为基础，第二向以蛋白质电荷差为基础
   C．两向电泳基础不定，可以任选
   D．两向电泳基础相同，只是方向不同
   E．以上都不正确

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

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.