The national average for an 8^thgrade reading comprehension test is 73. A school district claims that its eighth-graders outperform the national average. In testing the school district's claim, how does one define the population parameter of interest?

A)The standard deviation of the score on the 8^thgrade reading comprehension test.

B)The proportion of 8^thgraders that scored above 73 on the reading comprehension test.

C)The number of 8^thgraders that took the reading comprehension test.

D)The mean score on the 8^thgrade reading comprehension test.