In the Model Y_i = ?₀ + ?₁X₁ + ?₂X₂ $\frac { \Delta Y } { \Delta X _ { 1 } }$

Multiple Choice

In the model Y_i = ?₀ + ?₁X₁ + ?₂X₂ + ?₃(X₁ × X₂) + u_i, the expected effect $\frac { \Delta Y } { \Delta X _ { 1 } }$ is

A) ?₁ + ?₃X₂.
B) ?₁.
C) ?₁ + ?₃.
D) ?₁ + ?₃X₁.