Bob's average golf score at his local course is 93.6 from a random sample of 34 rounds of golf. Assume that the population standard deviation for his golf score is 4.2. The 90% confidence interval around this sample mean is:_______.
a. (92.4, 94.8).
b. (89.0, 98.3).
c. (90.5, 96.7).
d. (93.2, 94.0).