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.

Asex is an explanatory variable; starting salary is response variable; area of specialization is possible confounding variable

Bsex and salary is explanatory variables; area of specialization is response variable

Csex is explanatory; salary and area of specialization are response

Dsex is response; salary is explanatory; area of specialization is possible confounding

Esex and area of specialization are response; salary is explanatory