Which type of semiautomatic action allows for the first round to be double action while subsequent rounds are fired single action?

The correct answer is the type of action known as double action semiautomatic. In this system, the first round is fired using a double action mechanism. This means that the trigger pull both cocks the hammer and releases it, allowing for the initial shot to be more challenging due to the greater force needed. Following the first round, the mechanism transitions to single action for all subsequent shots. This is because the firing mechanism's action resets after the first shot is fired, meaning that the hammer is already cocked for the next round, resulting in a lighter and shorter trigger pull compared to the first shot.

This reference to double action semiautomatic mechanisms highlights the unique feature where the initial shot requires a different action from the subsequent shots, allowing for quick follow-up shots with less effort on the trigger pull. Other types of semiautomatic actions listed don't possess this specific combination of functionality, making double action semiautomatic the correct choice.