For the hypothesis tests described below in parts (a) through (c), one of which is the same as that described in Exercise 9.31a, identify what the critical z value would have been if there had been just one sample and we knew the mean and standard deviation of the population: 

a. A single-sample t test examining scores for 26 participants to see if there is any difference compared to the population, using a p level of 0.05 

b. A one-tailed, single-sample t test performed on scores on the Marital Satisfaction Inventory for 18 people who went through marriage counseling, using a p level of 0.01 

c. A two-tailed, single-sample t test, using a p level of 0.05, with 34 degrees of freedom 

d. Comparing the critical t value from 9.31 a with the critical z value from 9.39 b, explain how and why these are different.