Which of the following accounts is classified as a current liability?

Accounts payable is classified as a current liability because it represents amounts a business owes to its suppliers or vendors for goods and services that have been received but not yet paid for. These liabilities are typically settled within a short period, usually within one year, making them a key component of a company's short-term financial obligations.

Current liabilities are essential for assessing a company’s liquidity, as they reflect the obligations that must be met in the near future through the use of current assets. In contrast, preferred stock and retained earnings are part of equity, and investments are generally classified as long-term assets, none of which represent immediate obligations of the company. Thus, accounts payable distinctly fits the category of current liabilities due to its nature of being payable in the short term.