What is the main idea of the passage?

About the time of World War I, sharp-eyed entrepreneurs began . . . to see ways to profit from the motorist's freedom . . . Shops could be set up almost anywhere the law allowed, and a wide variety of products and services could be counted on to sell briskly in the roadside marketplace. A certain number of cars passing by would always be in need of gas. Travelers eventually grew hungry, tired, and restless for diversions. Soon gas stations, produce booths, hot dog stands, and tourist camps sprouted up along the nation's roadsides to capitalize on these needs. As competition increased, merchants looked for new ways to snag the new market awheel. Each sign and building had to visually shout: "Slow down, pull in, and buy. "Still more businesses moved to the highway— supermarkets, motor courts, restaurants, miniature golf courses, drive-in theaters. By the early 1950s, almost anything could be bought along the roadside.

Source: Excerpt from Chester H. Liebs, Main Street to Miracle Mile. Little, Brown and Company, 1985.

Miniature golf was a very popular sport in the 1950s.

Travelers were looking for sources of entertainment.

Some highway businesses were more successful than others.

Flashy commercial enterprises sprouted along highways, eager to profit from travelers.

The first businesses to flourish along the high-ways were gas stations and hot dog stands.

Choice d best describes the main idea of the paragraph

Was asked in this test : Social Studies Pre 1