The correct answer is:
b. A railroad that connects two cities.
The definition of interurban is a railway or train working or traveling between different cities.
The interurban is also a certain type of electric railway, including streetcar-like light electric railcars that are self-propelled. And they run within and between cities or towns. They were widespread in North America between 1900 and 1925 and were employed mostly for passenger travel between cities and their surrounding towns.
