The Percent of Students in a School Taking the Test

The percent of students in a school taking the test is important in understanding a school's test results because

A) the higher the percent of students taking the test, the higher the school's average score will be
B) the lower the percent of students taking the test, the lower the school's average score will be
C) the lower the percent of students taking the test, the higher the school's average score will be because the school will have discouraged those they expect to be low scoring from taking the test
D) it doesn't matter because the tests test individual knowledge