A market order is the order type most likely to ensure immediate execution because it instructs the broker-dealer to buy or sell at the best available current market price. If the investor’s primary objective is execution today rather than a specific price, a market order is the correct choice. Choice C is correct. A stop order becomes a market order only after the stop price is reached; if the stop price is not triggered, the order may not execute. A limit order specifies the minimum sale price or maximum purchase price, so execution is not guaranteed unless the market reaches the limit price and there is sufficient liquidity. A stop-limit order is even less certain because, after activation, it becomes a limit order rather than a market order. The SIE outline includes order types such as market, stop, limit, and good-til-canceled orders under Orders and Strategies. The technical trade-off is execution certainty versus price certainty. Market orders prioritize execution, while limit and stop-limit orders introduce conditions that may prevent execution. Reference: Section 3.1.1 Orders and Strategies.