参考答案：A

解析：

Opportunity cost is the return that a firm’s resources could have earned elsewhere in their next most valuable use. Opportunity cost includes both explicit and implicit costs. Explicit costs are observable, measurable expenses such as the dollar cost of production inputs and the interest cost of renting (borrowing) capital. Implicit costs are not explicitly observable and fall into two categories : (1) the opportunity cost to a firm of using its own capital and (2) the opportunity cost of the time and financial resources of the firm’s owners. Economic profit considers both explicit and implicit costs. When the firm’s revenues are just equal to its opportunity costs (explicit and implicit costs, including a normal profit) , economic profits are zero. Accounting profit considers only explicit costs but not implicit cost and normally exceed economic profit.