The correct answer is B. Portuguese ports now had exclusive control of Indian Ocean trade.
The cartaz system, introduced by the Portuguese in the early 16th century, represented a significant shift in trade practices. It was a passport system that allowed Portuguese colonial authorities to exert control over trade routes in the Indian Ocean by requiring all ships to obtain a cartaz to prove they were authorized to trade. This system effectively aimed to monopolize trade and exert influence over the region, marking a departure from previous, more open trade practices where various traders freely engaged in commerce without such controls.