病毒的持续感染是动物长期或终生带毒，但无明显临床症状的感染。
参考答案：对
By the time I swa the angry expression on his face, I ______ exactly what I was having to face. But not for a moment _______ I should quit.
A．had known; I thought
B．have known; had I thought
C．would know; I would think
D．knew; did I think
避雷器型号YH5WZ1-17/45中“Z”表示的意义是（）。
A.配电
B.变电站
C.电容器
D.铁路
