Gene and Rory get together and start a mortgage brokerage business. They each contribute $$25,000$ of capital to the business. After the first year of operation, the total owners' equity is listed as $$60,000.$ Most likely, the additional $$10,000$ of owners' equity is

a$.$ long$-$term liabilities

b$.$ common stock

c$.$ current liabilities

d$.$ retained earnings

e$.$ a bank loan