The correct answer is D. Relatively elastic demand.
Demand is elastic when a small change in price leads to a large change in quantity demanded. In other words, consumers are very sensitive to changes in price. This is often the case for goods that are not essential, such as luxury items.
When the demand for a good is elastic, a decrease in price will lead to an increase in quantity demanded, and an increase in price will lead to a decrease in quantity demanded. This is because consumers are willing to buy more of the good when it is cheaper, and less of the good when it is more expensive.
Perfectly elastic demand is a theoretical concept in which consumers are infinitely sensitive to changes in price. In this case, a small change in price would lead to an infinite change in quantity demanded. This is never actually observed in the real world, but it can be a useful approximation for some goods.
Perfectly inelastic demand is another theoretical concept in which consumers are completely insensitive to changes in price. In this case, a change in price would have no effect on quantity demanded. This is also never actually observed in the real world, but it can be a useful approximation for some goods.
Relatively inelastic demand is a situation in which the demand for a good is not very sensitive to changes in price. In this case, a change in price will lead to a smaller change in quantity demanded than would be the case for a good with elastic demand. This is often the case for goods that are essential, such as food and water.
I hope this explanation is helpful!