The law of demand states that there is an inverse relationship between the price of a good and the quantity demanded. In other words, as the price of a good decreases, the quantity demanded increases, and vice versa.

Option 1 states that there are no changes in the taste and preferences of consumers. This assumption is necessary for the law of demand to hold true. If consumers` preferences change and they no longer desire a certain good, the demand for that good will decrease, regardless of its price.

Option 2 states that the income of consumers remains constant. This assumption is also necessary for the law of demand to hold true. If consumers` income increases or decreases, their purchasing power changes, which can affect the quantity of goods they demand.

Option 3 states that consumers are affected by the demonstration effect. This option is the correct answer, as it is not an assumption in the law of demand. The demonstration effect refers to consumers` desire to imitate or emulate the consumption patterns of others. While the demonstration effect can influence consumer behavior, it is not a necessary condition for the law of demand to hold true.

Option 4 states that there are no changes in the price of substitute goods. This assumption is necessary for the law of demand to hold true