The value of a correlation is reported by a researcher to be r = -0.5. Which of the following statements is correct? Select one: a. The x-variable explains 50% of the variability in the y-variable. b. The x-variable explains 25% of the variability in the y-variable. c. The x-variable explains -25% of the variability in the y-variable. d. The x-variable explains -50% of the variability in the y-variable