Free SAT Practice Question

Before the 1880s, a traveler crossing the country reset a pocket watch town by town. Each community kept its own time by the sun, so noon in one city fell minutes after noon in the next, and a single rail line might pass through dozens of local times. Printing a workable schedule became nearly impossible when every station along a route counted the hour differently. In 1883 the railroads themselves imposed a fix, dividing the map into a handful of standard zones in which every clock would read alike. The tangle of local time gave way, almost overnight, to the system we still keep.

Which choice best describes the overall structure of the text?