evaluate the average income of US students one year after graduating from college

A researcher wants to evaluate the average income of US students one year after graduating from college.

a. If the researcher had taken 100 samples of 30 students who graduated a year ago from around the US and recorded their mean cost of attendance, would a distribution of his results be considered a sampling distribution? (2 pts)

b. If the researcher obtained a sample of 100 UT students who graduated a year ago, would a distribution of his results be considered a sampling distribution? (2 pts)

c. Which distribution would more accurately help you determine the mean income of all US students one year after graduating? Why is it more accurate? (2 pts)