Based on the Following Regression Equation (Standard Errors in Parentheses

Multiple Choice

based on the following regression equation (Standard errors in parentheses, n = 150) :
Q_D = 1000 - 50P_A + 10P_B + .05I, (20) (7) (.04)
where Q_D = quantity demanded of good A, P_A = price of good A, P_B = price of a competing good B, and I = per capita income.
-For which of the following variables should a "two tail" t-test be applied?

A) P_A
B) I
C) P_B
D) Should be applied for all.