The correct answer is: A. more quantity demanded at a lower price.
Extension of demand refers to the increase in the quantity demanded of a good or service due to a decrease in its price. This is because, when the price of a good or service decreases, consumers are able to afford more of it, and therefore demand more of it.
Option B is incorrect because it refers to the increase in the quantity demanded of a good or service due to an increase in its price. This is known as the law of demand, which states that, all other things being equal, the quantity demanded of a good or service will decrease as its price increases.
Option C is incorrect because it refers to the increase in the quantity demanded of a good or service due to a change in other factors, such as consumer income or the prices of other goods and services. This is known as a shift in the demand curve.
Option D is incorrect because it is not a valid option.