Explanation: The Indian Ocean trade network depended primarily on one thing: monsoons. These seasonal wings pushed boats from west to east in one part of the year, and from east to west six months later. The network was driven by the need for trade, not military conquest, so eliminate (A). Choice (C) is incorrect, as there was no competition with Europe. In fact, at the time, the Indian Ocean was far busier a trade route than any route in Europe. The development of the port cities was actually a function of there being a thriving trade network, not a cause of it, so (D) is incorrect. Choice (B) is the answer.