引起疱疹性咽峡炎的常见病原为
A.白色念珠菌
B.金黄色葡萄球菌
C.单纯疱疹病毒
D.链球菌
E.柯萨奇病毒
参考答案：E
During the flood many students volunteered ________ through the weekend, giving out food and water for the victims.
A．working
B．to work
C．to have worked
D．having worked
在原子吸收分析法中，被测定元素的灵敏度、准确度在很大程度上取决于（）。
A.空心阴极灯
B.火焰
C.原子化系统
D.分光系统
E.检测系统
