Final answer:
When the demand for a good or service increases, the equilibrium price and quantity both increase.
Step-by-step explanation:
When the demand for a good or service increases, the result is option D: Equilibrium price increases and quantity increases. This is because when demand increases, buyers are willing to pay a higher price for the good or service, resulting in an increase in price. As a result, suppliers are motivated to produce more of the good or service to meet the higher demand, leading to an increase in quantity supplied.