A regression model is to be fit using year in high school -- freshman, sophomore, junior, senior -- as an explanatory variable. How many variables will need to be included in the regression model to represent year in high school?

a. 1

b. 2

c. 3

d. 4

e. 5

Is the correct answer ' 5'?

Is the correct explanation: when using a regression model you should have one response variable and X explanatory variables. In this case, if you have 4 explanatory variables then you should have 5 variables total.

OR

Is the answer '3'?

Because in a regression model you have one variable less than the amount of explanatory variables? .. Isn't this the reasoning for Dummy variables?