The flu is believed _____ by viruses that like to reproduce in the cells inside the human nose and throat. [ ]

A. causing

B. being caused

C. to be caused

D. to have caused

急性咽后脓肿表现为（）。

A.多见于婴幼儿

B.多由咽后隙化脓性淋巴结炎引起

C.可引起呼吸困难

D.致病菌为金黄色葡萄球菌，乙型溶血性链球菌

E.咽后壁一侧隆起