Choice "B" is correct. A shift left in any demand curve represents a decrease in demand (at all price levels) for that product. Because gasoline and cars are considered complementary goods, the demand for gasoline is directly impacted by the demand for cars. If the price for cars increases, the demand for cars will decrease, causing the demand for gasoline to decrease, and the gasoline demand curve to shift left.
Choice "a" is incorrect. An increase in the price for gasoline will decrease the quantity demanded but will not affect overall demand across all price levels and quantities (as represented by a left shift in the demand curve).
Choice "d" is incorrect. A change in the supply curve will not cause a shift in the demand curve.
Choice "c" is incorrect. A decrease in the price of cars would have the opposite effect and cause a right shift in the demand curve.