埋弧焊机的负载持续率通常为().
A.50%
B.80%
C.100%
参考答案:C
Today is my birthday and my mother _______ a cake _______ me.
A.making, to
B.is making, for
C.is doing, to
D.doing, for
反映支气管哮喘患者气道反应性的检查是()
A.通气功能
B.支气管激发试验
C.峰流速变异率
D.嗜酸细胞阳离子蛋白
E.皮肤过敏原试验