For each of the problems described below, which are the same as those described in Exercise 9.21, 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 values with the critical z values, explain how and why these are different.