It is said that ____ young people may lose the abilities to hear after five years if they listen to MP4 players which are too loud for more than five hours a week.

A．thousand of

B．six thousands

C．thousands of

D．six thousands of

下图甲、乙别分表示人体内局部组织结构及其相关生理活动示意图，请据图回答下列问题：

人在感染某些细菌的初期，甲图血液中的（）细胞会在一定程度上杀灭细菌，这种免疫属于（）。