C ． 2Fab 和 pFc ′                                                   D ． 2Fab 和 Fc

12 ．引起婴幼儿急性肠炎的弯曲杆菌主要是 (       )

A ．空肠弯曲菌                                                       B ．胎儿弯曲菌

C ．幽门螺旋菌                                                       D ．绿脓杆菌

13 ．肺炎链球菌致病的主要物质是 (       )

A ．神经氨酸酶                                                       B ．链球菌溶血素 O

C ．鞭毛                                                                 D ．荚膜

14 ．在肠热症患者病程第一周时，分离培养沙门氏菌阳性率最高的标本是 (       )

A ．血液                                                                 B ．粪便

C ．尿液                                                                 D