Let x1 represent a quantitative independent variable and x2 represent a dummy variable for a 2-level qualitative independent variable. Which of the following models is the equation that produces two parallel curves, one for each level of your QL variable?

A. E(y) = ?0 + ?1x1 + ?2x12 + ?3x2
B. E(y) = ?0 + ?1x1 + ?3x2
C. E(y) = ?0 + ?x11 + ?3x2 + ?4x1x2
D. E(y) = ?0 + ?1x1 + ?2x12 + ?3x2 + ?4x1x2 + ?5x12x2