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．be have caused

某企业的产品销售量很小，但其价格高昂。那么这个企业很可能处于( )。

A．启动阶段
B．成长阶段
C．成熟阶段
D．衰退阶段