If a researcher believes that the effect of earning a Graduate degree on salary depends on gender, which of the following variables should she add to her dataset to test this hypothesis? 0 a. An interaction tem1 between the gender dummy and salary. O b. An interaction term between the Graduate degree dummy, the gender dummy and salary. O c. An interaction tem1 between the Graduate degree dummy and salary. O d.An interaction term between the gender dummy and the Graduate degree dummy