Which type of ladder features two hooks on a spring mechanism?

The correct answer highlights the distinctive features of a roof ladder, which is specifically designed for firefighting operations, particularly when accessing roofs. A roof ladder is characterized by its two hooks on a spring mechanism, allowing the ladder to securely hook onto the roof's ridge or peak. This mechanism helps stabilize the ladder and provides firefighters with a safe and reliable platform to work from when performing tasks such as ventilating a roof or performing rescue operations.

Roof ladders are essential for preventing slippage or falling during high-stakes situations, thereby ensuring the safety of the firefighters. In contrast, other types of ladders, such as extension ladders and step ladders, do not incorporate this specialized hook mechanism, as their designs are tailored for different applications and environments. The folding ladder also lacks these features, as it is typically designed for more general use. Thus, the uniqueness of the roof ladder's design and functionality makes it the correct choice for this question.