The more demand there is for something, the easier it is to sell. Any junkyard will buy a used car that is less than ten years old, because the parts can easily be resold. However, because there is little demand for car parts that are ten years old or older, junkyards tend not to buy those cars. Thus, used cars that are less than ten years old are generally easier to sell than are cars that are ten years old or older. Which one of the following is an assumption on which the argument depends? ['The salability of something is not influenced by any factors other than the level of demand for it.', 'All used cars that are ten years old or older are sold to junkyards.', 'When determining the selling price of cars less than ten years old, the lack of demand would not be offset by a lack of supply.', 'The salability of cars that are ten years old or older is largely a function of the level of demand for their parts.']