A railroad crossing (RC) consists of one or more rail tracks that intersect a street. The crossing is protected by a gate that must be operated automatically in such a way that cars cannot enter the crossing While a train is going through it. • Describe the structure of the railroad-crossing control system by showing its components and their interfaces. • State clearly and precisely the requirements that should be satisfied by the system in order for it to operate safely and usefully. For instance, deciding to keep the gate always closed would be safe, but useless, since no car could ever cross the track. • Which features of the system are likely to change in different contexts?