参考答案：C

解析：

A particular brand of toilet paper likely has elastic demand because there are many available substitutes. The existence of many substitutes indicates elastic demand. When good substitutes for a product are available, a price rise induces many consumers to switch to other products. Thus, if the price of a brand of toilet paper increases, total expenditure on that brand will likely decrease as consumers substitute cheaper brands. The most important determinant of the price elasticity of demand is the availability of substitutes. The other statements are true. The second law of demand suggests that in general, when the price of a product increases, consumers take time to reduce their consumption. Thus, demand decreases by a larger amount in the long run than in the short run. The demand for gasoline is likely inelastic. Thus, when price increases, the percentage change in quantity demanded is less than the change in price (and total expenditures on the good increase). The demand for an individual firm is more elastic than the demand for the entire market.