Final answer:
Money functions as a unit of account, allowing for easy comparison of economic values and simplifying trade-offs by acting as a common accounting method. Option a is the answer.
Step-by-step explanation:
Money serves as a unit of account, which means that it is the ruler by which we measure economic values. For example, an accountant may charge $100 to file your tax return. That $100 can purchase two pair of shoes at $50 a pair, facilitating the comparison of relative prices of goods and services.
Money acts as a common denominator, an accounting method that simplifies thinking about trade-offs, as opposed to barter, which would require a double coincidence of wants. This means each party in a trade must have what the other desires, which is vastly inefficient compared to using money as a medium.