Final answer:
The advance warning sign at a highway-rail intersection advises drivers to slow down, look, and listen for approaching trains.
Step-by-step explanation:
The subject of this question is Driving. The question is asking about the advance warning sign at a highway-rail intersection and its purpose. The advance warning sign is the first sign that drivers see when approaching a railway crossing. It serves to advise drivers to slow down, look, and listen for any approaching trains. Drivers should be prepared to stop if necessary.