儿童细菌性结膜炎最常见的致病菌是（）
A.肺炎双球菌
B.流感嗜血杆菌
C.摩拉克菌
D.金黄色葡萄球菌
E.肺炎链球菌
参考答案：B
____ he met with the difficulty did he realize that our help was of great importance
A．It was only when
B．Never until
C．Only before
D．It was not until
供水单位采购饮用水消毒产品时，应当索取消毒产品（）批准文件。
