The 6% interest rate represents an opportunity cost because it is the return Wei Zhang gives up by withdrawing the funds from the bank to purchase the automobile.

Key Concepts:

• Opportunity Cost: The value of the next best alternative forgone when making a decision. In this case, the 6% interest is what Wei Zhang sacrifices by using the funds for the car purchase instead of keeping them in the bank.
• Discount Rate: Typically used to calculate present values of future cash flows, not applicable here.
• Financing Cost: Would be the cost of borrowing money, but Wei Zhang is using his own funds, not borrowing.

Why C is correct: The interest earned on the deposited funds represents the forgone benefit that could have been earned if the money remained in the bank, which is the classic definition of opportunity cost.