Tell Whether a Linear Model or a Quadratic Model Is $x ^ { 2 }$

Multiple Choice

Tell whether a linear model or a quadratic model is appropriate for the data. If linear, tell whether the slope should be positive or negative. If quadratic, decide whether the leading coefficient a of $x ^ { 2 }$ should be positive or negative.
-The amount of sales tax paid as a function of the sales price.

A) quadratic; negative
B) linear; positive
C) linear; negative
D) quadratic; positive