Explanation:

1. Elastic Demand:
In economics, the elasticity of demand measures the responsiveness of the quantity demanded of a good or service to a change in its price. Elastic demand means that the quantity demanded is highly responsive to changes in price. When the demand for a good or service is elastic, a small change in price leads to a relatively large change in quantity demanded.

2. Flatter Demand Curve:
A flatter demand curve indicates that the quantity demanded is more responsive to changes in price. In other words, a small change in price leads to a relatively large change in quantity demanded. This is characteristic of elastic demand.

3. Explanation of Option D:
Option D states that the demand curve is flatter in case of relatively more elastic demand. This means that a small change in price will lead to a relatively large change in quantity demanded.

4. Visual Representation:
To understand this concept visually, imagine a demand curve on a graph with price on the y-axis and quantity on the x-axis. In case of elastic demand, the demand curve will be relatively flatter. This means that a small change in price will result in a large change in quantity demanded.

5. Example:
For example, let's consider the demand for a luxury car. If the price of the luxury car decreases by 10%, the quantity demanded may increase by 20%. This shows that the demand for luxury cars is relatively more elastic, as a small change in price leads to a relatively larger change in quantity demanded.

6. Importance of Elasticity:
Understanding the elasticity of demand is important for businesses and policymakers. Businesses need to know how responsive consumers are to changes in price in order to make pricing and production decisions. Policymakers use elasticity to determine the impact of taxes or subsidies on consumer behavior and revenue.

Conclusion:
In conclusion, the correct answer is option D, which states that the demand curve is flatter in case of relatively more elastic demand. This means that a small change in price will lead to a relatively large change in quantity demanded.