Explanation
The argument assumes that the primary factor determining the saleability of used cars to junkyards is the demand for the cars' parts. This underlies the reasoning that cars less than ten years old are easier to sell because their parts are in demand, whereas older cars are not due to a lack of demand for their parts.
A. The argument does not necessarily depend on the idea that no other factors influence saleability; it only posits that demand is a significant factor.
B. The argument does not claim that all cars older than ten years are sold to junkyards, only that there's a general trend against purchasing older cars due to lower demand for their parts.
C. The age-to-saleability correlation is specific to the context of junkyards and car parts, not a general statement about all items.
D. The argument does not discuss how the pricing of cars is determined or whether lack of demand might be offset by a lack of supply.
E. (Correct Response) The argument is built on the premise that the saleability of cars, particularly to junkyards, hinges on the demand for their parts. This premise must hold true for the argument to maintain that cars over ten years old are harder to sell because it is implied that the lack of demand for parts from such cars influences junkyards' purchasing decisions.
The necessary assumption for the argument's validity is that the saleability of cars to junkyards is primarily a function of the demand for their parts, which is directly stated in option E.