【正确答案】 A

【答案解析】[听力原文]
During the first half of the nineteenth century much thought was given to building the Panama Canal. The discovery of gold in California in 1848 brought an increased demand for a transportation link across Panama. A railroad line was completed after six years of hard labour in the swamps and jungles. Over two thousand workmen died from yellow fever and malaria. In 1881, a French organization tried to build a canal across the Isthmus. For eleven years, workmen struggled against heat and disease. At least 15,000 died before the French gave up their attempts to build the canal. For years the abandoned machinery lay in the jungles. At the close of the Spanish-American War, the United States bought a strip of land ten miles wide across the Isthmus. Immediate attention was given to the control of diseases. In two years, yellow fever was completely eliminated. Because of the work of American medical heroes, it was possible to build the splendid Panama Canal.