When considering a business's capital structure, which of the following statements is true regarding the weighted average cost of capital $($WACC$)?$

WACC decreases as a company's debt$-$to$-$equity ratio increases.

WACC represents the average cost of all sources of capital weighted by their respective proportions in the capital structure.

WACC is primarily used to assess a company's profitability.

WACC is unaffected by changes in a company's debt$-$to$-$equity ratio.