45. _______________ First, the United States had to pay France for the work it had already done on the canal. Second, the United States had to get permission from Columbia to build on its soil. Finally, many workers died of yellow fever, and the United States had to find a method to rid the area of mosquitoes, which caused the deadly disease.
(A) The Panama Canal was built by the United States under a treaty.
(B) The Panama Canal has made a great contribution to American economy and played a vital role in world commerce.
(C) The Panama Canal was hailed as the best-constructed canal in the world.
(D) Building the Panama Canal was a difficult and expensive task for the United States.