She has a gift for creating an atmosphere for her students ____allows them to communicate freely with each other.

A．which

B．where

C．what

D．who

下列哪项试验不是凝集试验（）

A.血型鉴定

B.肥达反应

C.病毒血凝试验

D.快速血浆反应素环状卡片试验

E.胶体金免疫层析试验