An Instructor in Introductory Psychology Wanted to Know If the Textbook

An instructor in Introductory Psychology wanted to know if the textbook she was using was as effective as other textbooks on the market. In order to test this, she decided that she would teach the course in the fall with the text she typically uses, and in the spring she would use a new text. After doing this, she compared the students' final grades and students' responses to an 'end of semester' evaluation question. The question was "How effective was the text for this course?" She discovered that students' grades increased from a mean of 78 in the fall to 83 in the spring. She also discovered that the students' opinion of the course's text increased from a mean of 4.5 (on a 7-point scale, the higher the better) in the fall to 4.9 in the spring. After running the appropriate statistical test(s) , she discovered that both of these differences were statistically significant.
If we see a relationship over time between television violence and children's expression of aggression, we could conclude that

A) violence causes aggression because people who watched violent television in third grade were also violent in third grade.
B) people who watched a lot of violence in third grade also watched violence in twelfth grade.
C) violence leads to aggression because violent TV is third grade was related to aggression in twelfth grade.
D) violence leads to aggression because being aggressive in third grade leads to watching violence in twelfth grade.