The correct answer is: A. Giffen goods.
Giffen goods are a type of inferior good, which means that demand for a good increases as its price increases. This is because consumers who buy Giffen goods are very poor and have very limited budgets. When the price of a Giffen good increases, it takes up a smaller share of their budget, leaving them with more money to spend on other goods. This increase in purchasing power leads to an increase in demand for the Giffen good.
Normal goods are goods for which demand increases as income increases. This is because consumers with more income can afford to buy more of these goods.
Articles of conspicuous consumption are goods that are bought not for their own sake, but for the social status that they confer on the buyer. Demand for these goods is not affected by changes in price.
Ignorance of the buyer can affect demand for a good, but it is not a fundamental exception to the law of demand. If a buyer is unaware of the existence of a good, they will not demand it. However, if they become aware of the good, they will demand it in accordance with the law of demand.
In conclusion, the only exception to the law of demand is Giffen goods.