A Factorial Design Would Be the Appropriate Method to Answer

A factorial design would be the appropriate method to answer which of the following research questions?

A) To determine whether average teacher salaries differ in Ohio, Pennsylvania, and Indiana.
B) To determine whether average teacher salaries differ in Ohio, Pennsylvania, and Indiana, controlling for salary differences across grade level.
C) To determine the effect of an additional year of experience on a teacher's salary.
D) To determine the joint effects of a teacher's field (math, English, etc.) and whether the teacher works in a public school or a private school on a teacher's salary.