A researcher wanted to determine whether eating hamburgers for lunch increased the aggression of second graders during their afternoon play period. after feeding a group of 20 students hamburgers for lunch she observed that, on average, the students committed 2.5 aggressive behaviors during their afternoon play period. in this example, which of the following describes the sample?

A The 2.5 aggressive behaviors
B The 20 students the researcher observed
C All second graders
D All second graders who ate hamburgers for lunch