A Professor Believes That Students Who Smoke Cigarettes Tend to Have

Multiple Choice

A professor believes that students who smoke cigarettes tend to have lower grades. He collects data from 1326 randomly selected students at his university and discovers that, on average, students who smoke cigarettes do indeed tend to have lower grade point averages than students who do not smoke.
Does this study give strong evidence that smoking cigarettes causes lower grades?

A) Yes, because the study included both people who smoked and people who didn't.
B) Yes, because the subjects in the study were selected at random.
C) No, because the study showed that there is no connection between smoking and grades.
D) No, because people who make bad decisions may choose not to study well and may choose to smoke cigarettes.
E) No, because the people in the study were not blinded.