An educator wanted to look at the study habits of university students. As part of the research, data was collected for three variables – the amount of time (in hours per week) spent studying, the amount of time (in hours per week) spent playing video games and the GPA – for a sample of 10 male university students. As part of the research, a 95% confidence interval for the average GPA of all male university students was calculated to be: (2.95, 3.10).

Which of the following statements is true?

a. In construction of the confidence interval, a z-value with 10 degrees of freedom was used.
b. In construction of the confidence interval, a z-value was used.
c. In construction of the confidence interval, a t-value with 10 degrees of freedom was used.
d. In construction of the confidence interval, a t-value with 9 degrees of freedom was used.