根据课文填空：

Before the middle of the 5th century, people in Britain all spoke a language called Celtic．Then three Germanic  __34____ from the __35____ mainland ---the Angles, the Saxons and the Jutes---- invaded Britain．They each had their own language and Anglo-Saxon developed from_mixing these languages with Celtic．At the end of 9th century, the Vikings,people from Scandinavian countries,___36___Damark and Norway began to invade Britain．They __37____with them their languages,which also mixed with Anglo-Saxon．The language they____38__is what we now call Old English．

分离分子量相近但等电点不同的蛋白质的最适方法为（）

A.琼脂糖凝胶电泳

B.圆盘电泳

C.等电聚焦电泳

D.醋酸纤维薄膜电泳

E.密度梯度离心