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The correct answer is C.
The WACC is considered as an opportunity cost for the firm. Therefore, a company can create value by producing returns that are greater than the cost of capital (WACC).
Options B and C are incorrect because taking on projects whose returns are below the WACC will decrease the value of the firm. For example, a one-year project that would return 1% when the cost of capital is 10% would decrease the value of the firm.