管式加热炉按传热方式可分为（）。
A、纯对流炉
B、辐射对流炉
C、辐射室炉
D、纯加热炉
参考答案：A, B, C
The world's population has grown _____ it was in 1800.[ ]
A. six times more than what
B. more than six times what
C. six times more than which
D. more than six times that
内毒素的基本成分是（）
A.糖蛋白
B.溶血毒素
C.类脂A
D.非特异核心多糖
E.O特异性多糖
