A researcher wants to include level of education as an independent variable in a logistic regression model. Level of education has eight categories(1) none, (2) some elementary school, (3) completed elementary school, (4) some high school, (5) completed high school, (6) some college, (7) completed college, and (8) graduate school. How many dummy variables does the researcher need to create to include this variable in the regression model?

a. 5

b. 6

c. 7

d. 8