?What is the parameter of interest in part? a)? A.the mean cost of a gallon of…

?What is the parameter of interest in part? a)?
A.the mean cost of a gallon of gas at a particular local gas station
B. The mean cost of a gallon of regular gas for all gas stations in this area
C. The cost of a gallon of regular gas at a local gas station
D. The mean cost of a gallon of regular gas for a random sample of 15 local gas stations