Final answer:
The correct answer is a) Cloud approaching, based on the description of environmental awareness and a focus on vigilance and safety similar to the scenarios provided.
Step-by-step explanation:
Based on the context provided in various narratives, and considering an alertness to the environment or welfare of children, the correct option for what Mary notices is a dark cloud approaching. This choice aligns with the description of anticipation and environmental awareness, similar to the way children and adults in one of the excerpts react to sombre clouds that signify an approaching storm.
The possibility of ringworm as observed on Sarah's arm, or a general vigilance towards hazards as discussed in the example with Susan and the children, supports the health and safety theme evident in the scenarios provided. Therefore, the narratives illustrate the importance of vigilance and immediate action when potential risks are identified, whether they be natural phenomena or other threats to health and safety.