Which of the control lights visible in the illustration upon lighting up, requires you to stop immediately and rectify the fault?

The red warning light B signals critically low engine oil pressure. You must then stop the vehicle immediately in a safe place and switch off the engine to prevent it from seizing. The amber warning lights (A - ABS fault, C - low fuel level) inform about malfunctions or the need to top up fluids, but usually allow you to continue driving to the nearest petrol station or garage.