Which scenario illustrates machine-to-machine (M2M) communication in the IoT?

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Machine-to-machine communication is when devices directly exchange data and trigger actions without human intervention, enabling real-time automation. In this scenario, the autonomous ambulance uses its onboard systems to talk with traffic signal controllers and request a change from red to green as it approaches an intersection. The lights adjust automatically in response to that machine-initiated signal, allowing the ambulance to proceed more quickly and safely. This shows M2M because the ambulance and the traffic lights coordinate directly through devices talking to each other, without a person deciding and acting. The other situations involve humans in the loop: a sensor suggesting action but a herd manager decides what to do, maintenance decisions based on sensor alerts, or a weather notification sent to a farmer—none of which are automated device-to-device actions.