In a multiple regression linear model, we can choose to include an interaction term between 2 or more of the explanatory variables. This allows the effect (.e. slope) of one explanatory variable to vary depending on the value of the other variable(s) in the interaction term. How should you write an interaction model in R's Im function to create a model with an interaction between 2 explanatory variables, x1 and 2? a. Im(x1 + x2 - y, data = some_data) b. Im(y - x1 * x2, data = some_data) c. Im(y - x1 + x2, data = some_data) d. Im(x1 * x2 - y, data = some_data)