A survey is to be administered to recent graduates of a certain nursing school in order to compare the starting salaries of women and men. For a random simple of graduates, three variables are to be recorded: sex, starting salary, and area of specialization.

a) sex is an explanatory variable; starting salary is response variable; area of specialization is possible confounding variable
b) sex and salary is explanatory variables; area of specialization is response variable
c) sex is explanatory; salary and area of specialization are response
d) sex is response; salary is explanatory; area of specialization is possible confounding
e) sex and area of specialization are response; salary is explanatory