In a First-Order Model with Two Predictors $x _ { 1 }$

In a first-order model with two predictors, $x _ { 1 }$ and $x _ { 2 }$ , which of the following best describes when an interaction term may be used?

A) When the relationship between the dependent variable and the independent variables is linear.
B) When the effect of $x _ { 1 }$ on the dependent variable is influenced by $x _ { 2 }$ .
C) When the effect of $x _ { 2 }$ on the dependent variable is influenced by $x _ { 1 }$ .
D) When the effect of $x _ { 1 }$ on the dependent variable is influenced by $x _ { 2 }$ or when the effect of $x _ { 2 }$ on the dependent variable is influenced by $x _ { 1 }$ .