The correct answer is D) iron and wood.
The raw materials that had to be shipped to the construction sites in large quantities because they were essential for building the railroad tracks were iron and wood.
The Pacific Railroad Act of 1862 allowed the construction of a transcontinental railroad to connect the East coast of the United States with the West coast. The Union Pacific Railroad and the Central Pacific were the two companies that could receive the task to accomplish this important feat. They worked for seven years to connect the railroads from Omaha, Nebraska to Sacramento, California, until they finally met on May 10, 1869, in Promontory Utah.