D. The Panama Canal shortened the travel time by ship between the East Coast and West Coast of the United States. Before the Panama Canal was built, ships had to sail around the southern tip of South America to travel between the two coasts, which was a much longer and more dangerous journey. With the opening of the Panama Canal in 1914, ships could travel directly between the two coasts through the canal, reducing travel time and costs. This made trade and commerce between the East Coast and West Coast more efficient, which in turn promoted economic growth on the West Coast of the United States.