English has become the most widely spoken language in the world ______ its special role(作用) as

an international language. [ ]

A. because

B. from

C. with

D. because of

某地夏季突然出现腹泻病人群，发病人数在数日内迅速增加，但临床症状不典型。细菌学诊断中对病原菌的检验方法有（）

A.分离培养

B.直接涂片镜检

C.血清学试验

D.动物试验

E.以上都是