What is the only environmental control located in the rear cockpit on the engine/electrical switch panel?

The evaporator blower control switch is the correct answer because it specifically manages the airflow from the rear cockpit's environmental control system. This switch allows the pilot in the rear cockpit to adjust the blower's operation, affecting the ventilation and climate control within that space.

The ram airflow switch, while relevant to controlling airflow based on the aircraft's speed and altitude, is typically located in the front cockpit and serves a different purpose. The bleed air inflow switch is also located in the front cockpit, managing air sourced from the engine bleed system rather than controlling airflow within the cockpit directly. Lastly, the temperature control rheostat adjusts the temperature, but it is responsible for regulating the environmental conditions rather than directly managing the airflow that the blower control switch does. This configuration underscores the specific role of the evaporator blower control switch in maintaining comfort and environmental conditions for the rear cockpit occupant.