低压断路器的脱扣器有很多种，其中（）起短路保护作用。
A.热脱扣器
B.电磁脱扣器
C.分夙脱扣器
参考答案：B
An analyst gathers the price-earnings ratios (P/E) for the firms in the S&P 500 and then ranks the firms from highest to lowest P/E. She then assigns the number 1 to the group with the lowest P/E ratios, the number 2 to the group with the second lowest P/E ratios, and so on. The measurement scale used by the analyst is best described as:（）
A. ordinal.
B. interval.
C. nominal.
大面积烧伤病人24h内主要的护理措施是( )
A．镇静止痛
B．心理护理
C．预防感染
D．保持呼吸道通畅
E．保证液体输入
