Final answer:
The nurse's priority is to ensure the client's safety and report the situation to adult protective services for further investigation and protection of the client.
Step-by-step explanation:
The priority nursing action after observing multiple areas of ecchymosis in various stages of healing is C. Ensure the client's safety and notify adult protective services. It is important to address the physical signs of potential abuse, as well as the client's statements which may imply neglect or mistreatment. The nurse must take immediate action to protect the client from further harm, which involves notifying appropriate authorities to intervene, assess, and provide the necessary protection and services for the client.