Several Studies Find That Among College Students, Use of Illegal

Several studies find that among college students, use of illegal drugs is negatively correlated with grade-point average. Which conclusion, if any, do these results justify?

A) The use of illegal drugs impairs either learning, memory, or concentration.
B) Highly conscientious students, who are likely to do well in school, avoid illegal drugs.
C) Students who spend their time and effort on risky activities do not spend much time studying.
D) The results do not justify any of these conclusions.