将抗体（抗原）、酶和戊二醛同时反应连接而成酶结合物的方法称为（）

A.酶结合物

B.戊二醛交联法一步法

C.戊二醛交联法二步法

D.过碘酸盐氧化法

E.Schiff碱

It is hard for the Greek government to get over the present difficulties ____ it gets more financial support

from the European Union.[ ]

 A. if

B. unless

C. because

D. since