小儿上呼吸道感染的病因错误的是

A．各种病毒和细菌均可引起

B．以病毒为多见，占60%

C．可继发细菌感染，最常见为溶血性链球菌、肺炎链球菌等

D．肺炎支原体也可引起

E．佝偻病、营养不良的小儿易患本病

When launching an open lifeboat by falls，the boathooks should be（）.

A.secured forward and aft where readily available

B.secured amidships where they will not hinder the personnel

C.used for fending off

D.used for picking up survivors in the water