Introduction:
The given analogy is "Fire Engine : Fire". To find the correct analogy for "Ambulance", we need to understand the relationship between a fire engine and fire.

Explanation:
- A fire engine is a specialized vehicle specifically designed to extinguish fires and provide assistance during fire emergencies.
- The purpose of a fire engine is to respond quickly to fires and provide necessary equipment and resources to control and extinguish them.
- The primary role of a fire engine is to ensure the safety of people and property by combating fires effectively.

Analysis:
Now, let's analyze the relationship between an ambulance and its corresponding function.

Ambulance:
- An ambulance is a specially equipped vehicle used for transporting sick or injured individuals to medical facilities.
- It is designed to provide emergency medical care and transport patients to hospitals or healthcare centers.
- The primary purpose of an ambulance is to provide immediate medical attention and ensure the well-being of patients during emergencies.

Conclusion:
Based on the analysis, the correct analogy for "Ambulance" is "Patients". Just as a fire engine is directly associated with fighting fires, an ambulance is directly associated with transporting patients during medical emergencies. Therefore, option A, "Patients," is the correct answer.