Anews story titled "auto sales zoom, by low prices at the pump" includes a graphic showing increasing car and truck sales in one panel and decreasing gasoline prices in the other panel. source: "auto sales zoom, by low prices at the pump," wall street journal, december 3, 2014. the graphic described assumes that autos and gasoline are
a. complements, because if the price of gasoline decreases, the demand for its complements, cars and trucks, increase.
b. complements, because if the price of gasoline increases, the demand for its complements, cars and trucks, increase.
c. substitutes, because if the price of gasoline decreases, the demand for its substitutes, cars and trucks, decrease.
d. substitutes, because if the price of gasoline decreases, the demand for its substitutes, cars and trucks, increase.