In Which of the Following Hypotheses Is the Independent Variable

Multiple Choice

In which of the following hypotheses is the independent variable (in other words, the temporal order or direction of influence) most clear?

A) The more often you interact with someone, the more you like him or her.
B) Students who have firm career goals achieve higher GPAs than those who do not have firm career goals.
C) The more often a student drinks, the more likely that he or she is depressed.
D) The greater the level of parent-child communication, the less likely that a child is delinquent.
E) Children who are breast-fed tend to have higher IQ scores than those who are not breast-fed.