Among the choices, common stock generally exposes an investor to the greatest market risk, so A is correct. Market risk (systematic risk) is the risk that overall market movements—driven by economic conditions, interest rates, investor sentiment, geopolitical events, and broad factors—will cause the value of an investment to fluctuate. Common stocks typically have the most direct exposure to business performance expectations and market sentiment, and they do not have contractual cash flows or principal repayment at maturity. Because common shareholders are residual owners, their value can be highly volatile and can decline significantly in adverse markets or company-specific downturns.

Preferred stock (choice B) is generally less volatile than common stock because it has a stated dividend and a senior claim over common in dividends and liquidation, though it still carries equity risk and rate sensitivity. Corporate bonds (choice C) are debt instruments with contractual interest payments and principal repayment at maturity; while they do have interest rate and credit risk and can fluctuate in price, they typically exhibit less market volatility than common stocks. U.S. government bonds (choice D) are generally considered to have low credit risk and often lower volatility relative to equities; their primary risk is interest rate risk rather than equity market risk, and they often behave differently than stocks during market stress.

On the SIE, this type of question tests the basic hierarchy: equities (especially common) are generally riskier and more volatile than debt, and within debt, U.S. government securities are typically viewed as having lower credit risk than corporate debt. Therefore, common stock is the best answer for greatest market risk exposure.