Which of the Following Was the Most Significant Contribution Made

Multiple Choice

Which of the following was the most significant contribution made by the U.S. Army Corps of Topographical Engineers during the first half of the nineteenth century?

A) The building of levees to protect the city of New Orleans
B) Its survey of the Oregon Trail
C) The surveying of possible routes for a transcontinental railroad
D) The expeditions it sponsored to explore the West