Suppose That the Demand Curves for Goods A,B,and C Have

Suppose that the demand curves for goods A,B,and C have the following functional forms:,where Q denotes quantity demanded and P denotes price: Q_A = 120 - 3.5P_A - 6P_B
Q_B = 100 - 2P_B + 3P_C
Q_C = 1500 - 0.5P_C.
Based on these demand curves,which of the following pairs of goods are known to be substitutes?

A) A and C
B) A and B
C) B and C
D) A and C,and B and C
E) none of the pairs are substitutes