What is the concept of Weighted Average Cost of Capital (WACC)?

A - It is the discount rate used to discount future cash flows when evaluating an investment plan.
B - The calculation of this rate is interesting or could be effective considering three different approaches: as an asset of the company, from the liability, and as investors.
C - It is the cost of production of a company.
a) Only A is correct.
b) A and B are correct.
c) A, B, and C are correct.