From what I can understand, I would say the statement that best describes the efforts required to complete the construction of the Panama Canal would be the second choice. The workers had to be recruited from different countries in the region. It's not the first choice, since there were no attacks whatsoever by any rebels groups (least not from what I can remember). It's not the third choice because there were no tensions between Panama and its neighbors to begin with, and it's not the fourth choice because immigrant laborers had no "engineering expertise" or experience, since they were merely just workers following given directions.
