An experimenter gives one group of depressed subjects the medication Prozac and another group of depressed subjects a placebo and measures the number of violent or suicidal thoughts members of both groups have. In this situation, the independent variable is
A) whether or not the medication is administered.
B) whether or not the subjects are depressed.
C) the number of violent thoughts the subjects report.
D) the number of suicidal thoughts the subjects report.