<em>The best answer is:</em><em> B) located along major trade routes.</em>
The first human settlements had began in the neolithic revolution, when men stopped being nomadic and they began to raise cattle and later they learned to cultivate. They chose the most fertile lands, generally bathed by large rivers.
People held the sedentarism, learned how to create artesanais, design new tools, etc. They increased the agricultural production and began to interchange their products. Then they had to organize socially, religiously, military, etc. The commerce between different settlements began to grow up and flue and then the commercial routes were created.
The principal earliest civilization began in Summer, Egypt, Indo Valley and Chinese Regions. Later, a lot of cities began to emerge in strategic points between those civilizations because they could take advantage of the commerce, and in consequence it impulsed the emergency of the route of the incense route, the silk route, etc.
When the Phoenician created a great navy and found the factories along the Mediterranean coasts the commercial and cultural change, Europe experimented and explosion of grown and prosperity.
Rome, Constantinople, London, New York, and a long etcetera become great cities by the same reason.
In that way the commerce was the main factor to the emergency and growing of the major important cities in the world.
