In which situations should you switch off the engine to save fuel and reduce environmental pollution?

You got the correct answers. Switching off the engine is recommended in situations where you have to wait for a longer, predictable period, such as during a traffic jam or at a gated railroad crossing. This reduces unnecessary fuel consumption and minimizes environmental pollution. However, at a "Stop" sign, the stop is typically brief and not long enough to justify shutting off the engine, so you should keep it running. Remember: Turn off your engine only when longer stationary periods are expected. This practice helps both the environment and fuel efficiency.