艾滋病被称为“人类的杀手”，它是由艾滋病病毒引起并主要通过血液进行传播，至今人类还没有找到根治该病的办法．从理论上讲，研制疫苗并进行预防接种是根除该病的最好对策，该对策的作用在于（　　）

A．控制传染源

B．切断传播途径

C．保护易感者

D．探究病毒结构

The person who is _______ of the factory _______ ill since last week.[ ]

A. in charge; has been

B. in the charge; has fallen

C. taking charge; was

D. in charge; fell