伪膜性肠炎（）。
A．真菌
B．红细胞
C．上皮细胞
D．白细胞增多
E．吞噬细胞增多
参考答案：C
A sample has 64 observations with a mean of 30 and standard deviation of 20. If the reliability factor is 2.05, the upper confidence limit for the population mean is closest to:（）
A. 30.64
B. 32.50
C. 35.13
