You are the sales manager for a large condominium development in Florida. From the 150 condos you have build, you took a random sample of 21 units. The average sales price of these 21 condos is 350,000 with a standard deviation of 20,000. The appropriate sampling distribution for constructing a 95% confidence interval for the average sales price of the population of equivalent condos is the... a) Student's t-distribution, with df= 20 b) Student's t-distribution, with df=22 c) Standard Normal Distribution d) Student's t-distribution, with df=21