I believe the answer is A. natural harbors provided a place to safely dock ships.
The middle age was in the duration from the 5th century to the 15th century.
The age began with the falling of the Western Roman Empire.
Throughout the era of the Western Middle age, church was the most important force in providing unity and stability.
The correct answer is the Suez Canal in Egypt.
The others are in different continents: The Grand Canal in Europe (Venice), the Panama Canal in the Americas ( and splits the two Americas) and Erie Canal is in America (NY).