Johanna Wants to Study the Effects of Study Guide Use

Johanna wants to study the effects of study guide use on general psychology student test scores. Which of the following represents the population, and which represents the sample for her study?

A) all possible general psychology students; current general psychology students enrolled at her university this semester
B) current general psychology students enrolled at her university this semester; all possible general psychology students
C) the current general psychology students enrolled at her university this semester; the general psychology students who actually participate in her study
D) the general psychology students who actually participate in her study; the current general psychology students enrolled at her university this semester