Which of the following questions is considered a size-up question in a crisis?

A size-up question is one that helps to quickly assess the current situation during a crisis, which is vital for effective decision-making and problem-solving. The question "What has happened?" directly addresses the immediate context of the crisis, allowing responders to gather essential information about the event. This understanding is fundamental as it sets the stage for all subsequent actions and analyses. Knowing what has transpired helps to establish the nature of the crisis, the implications of the incident, and the urgency of the response needed.

Other options focus on specific elements relevant to the crisis. The question regarding how many people are involved provides important quantitative data but does not give a comprehensive overview of the incident itself. Similarly, asking about resources lacking or solutions already considered, while important in their own right, both presuppose a level of understanding about the crisis that only the foundational question "What has happened?" can provide. Thus, it’s crucial to first establish the situation before delving into details about resource gaps or prior considerations.