The question is incomplete. The complete question is :
Members of a research team are considering three studies related to sleep and learning. The first study involves comparing the scores on a post-study test of learning from two groups of randomly chosen adults, with one group getting at least 7 hours of sleep per night for a week and the other group getting at most 6 hours of sleep per night for a week. A second study involves asking a random sample of students at a large university to report the average number of hours of sleep they get each night and their college grade point average. A third study involves asking a random sample of high school students in a large school district whether they feel they get enough sleep to stay alert throughout the school day.
Which study appears to look for an association between two variables without actively manipulating either one. What are those variables ?
Solution :
The second study in the context is involved in asking for a random sample of the students at an university to provide a report the average hours of sleep that everybody get each night and also the grade point of their college appears for association between these two variables without actively changing either of one.
These variables are the grade point average of the students and the numbers of hours of sleep.