Marginal cost of capital is the cost of: ?

<p style="text-align:justify;">(<strong>a) Additional Sales,</strong></p> <p style="text-align:justify;"><strong>(b) Additional Funds,</strong></p> <p style="text-align:justify;"><strong>(c) Additional Interests,</strong></p> <p style="text-align:justify;"><strong>(d) None of the above.</strong></p>