单选题 For a t- distributed test statistic with 30 degrees of freedom, a one -tailed test specifying the parameter greater than some value and a 95 percent confidence level, the critical value is:

A. 1.697.
B. 1.640.
C. 2.042.

【正确答案】 A

【答案解析】This is the critical value for a one - tailed probability of 5% and 30 degrees of freedom.