What is the primary reason that changes in a firm's capital structure can change the cost of its capital?

a$.$ A changing in the capital structure of a firm requires board approval, which costs the firm money to

facilitate.

b$.$ Each type of financing has a different cost that contributes to the overall cost of capital.

c$.$ There are different flotation costs associated with the different types of financing.

d$.$ Each type of financing has different tax implications.