In each case, specify which of the two variables is the explanatory variable and which is the response variable. If it is ambiguous, explain why.
a. Is there a relationship between eye color and whether or not corrective lenses are needed by age 18?
b. For women who are HIV-positive when they get pregnant, is there a relationship between whether or not the HIV is transmitted to the infant and the length of time the woman had been infected before getting pregnant?
