A researcher gives different amount of X to different subjects and then measures how much Y each subject produces. She finds that subjects who got more X produce more Y and subjects who got less X produce less Y. She also finds no other variable that can account for the different amounts of Y that the subjects produce. What conclusion should she draw?
a. There is a relationship between X and Y.
b. There is a relationship between Y and X.
c. X causes Y.
d. Y causes X.
e. A confounding variable, Z, causes both X and Y.
f. There is not enough information to draw any conclusion.