The correct answer is D.
Economics is a social science that studies the production, distribution, and consumption of goods and services. It is a positive science, which means that it seeks to explain the world as it is, not as it should be. Economics can be used to analyze the consequences of different policies, choices, or conditions, but it cannot tell us what kind of economic behavior or policy is right or wrong.
Option A is incorrect because economics cannot prove that capitalism is better than socialism. Economics can be used to analyze the consequences of different economic systems, but it cannot tell us which system is better.
Option B is incorrect because economics does not tell us what kind of economic behavior or policy is wholesome and what is evil. Economics is a positive science, which means that it seeks to explain the world as it is, not as it should be.
Option C is incorrect because economics does not tell policy makers which alternative to choose from among several efficient ones. Economics can be used to analyze the consequences of different policies, but it cannot tell us which policy is the best.