单选题 Ken Wallace is interested in testing whether the average price to earnings (P/E) of firms in the retail industry is 25. Using a t - distributed test statistic and a 5% level of significance, the critical values for a sample of 40 firms is/are:

A. -1.685 and 1.685.
B. -1.96 and 1.96.
C. -2.023 and 2.023.

【正确答案】 C

【答案解析】There are 40-1=39 degrees of freedom and the test is two - tailed. Therefore, the critical t - values are ±2.023. The value 2.023 is the critical value for a one -tailed probability of 2.5%.