ICS develops in a ______ fashion based on an incident's size, complexity, and hazard environment.

The correct answer emphasizes that the Incident Command System (ICS) is designed to be modular. This modular approach means that the system can expand or contract based on the incident's specific needs, which include its size, complexity, and the hazards present.

This flexibility allows for different sections, branches, or divisions to be added or scaled back as required by the situation at hand. For instance, a small incident may only need a few resources, whereas a larger or more complex incident may require additional personnel and equipment across various functional areas. The modular structure enhances operational efficiency and ensures that all tasks can be effectively managed without overwhelming the system.

In contrast, a purely systematic or static model would not allow for such adaptability, which is essential in dynamic emergency situations. Additionally, a rapid approach may suggest urgency but doesn't capture the inherent scalability and customization that the modular system provides. Thus, the modular characteristic is fundamental to the functionality and effectiveness of the ICS in effectively managing incidents.