In 1920, after some thirty-nine years of problem with disease, high costs and politics, the Panama Canal was officially opened finally linking the Atlantic and Pacific Oceans by allowing ships to pass through the fifty -mile Canal Zone instead of traveling some seven thousand miles around Cape Horn, It takes a ship approximately eight hours to complete the trip through the canal and costs an average of fifteen thousand dollars . one-tenth of what it would cost an average ship to round the Horn . More than fifteen thousand ships pass through its locks each year. The French initiated the project but sold their rights to the United States, which actually began the construction of the project The latter will control it until the end of the twentieth century when Panama takes over its duties.
The word 'locks' in the third sentence is closest in meaning to
