The cost of equity capital is all of the following except:

a$.$

The minimum rate that a firm should earn on the equity$-$financed part of an investment.

b$.$

A return on the equity$-$financed portion of an investment that, at worst, leaves the market price of the stock unchanged.

c$.$

By far the most difficult component cost to estimate.

d$.$

Generally lower than the before$-$tax cost of debt.