Which of the following defines internal rate of return (IRR)?

a. IRR is the difference between the present value of the cash inflows and outflows associated with a project.

b. IRR is the total variable cost incurred in a project.

c. IRR is the interest rate that sets the present value of a project's cash inflows equal to the present value of a project's cost.

d. IRR is the maximum return achievable on investments.