The correct answer is "D"
Railroads laid the path for the development of the western part of the country. They also served as a mean of transportation for commodities that were produced from the mining industry. At the same time, they depended on the steel industry in order to further expand their networks throughout the country.
On the other hand, grocery chain stores are a product of the technological developments in the field of processed foods. This industry emerged during the 2oth century with the introduction of corn syrup.
