The sailors followed ___ across the Indian Ocean that had been established hundreds of years before by spice merchants.trade routesscurviescircumnavigation

The correct answer is "trade routes."

Explanation:

The sentence refers to established paths used by sailors, particularly in the context of maritime travel across the Indian Ocean. "Trade routes" are networks of paths or waterways that have been historically used for the exchange of goods, including spices, which were highly valued and sought after.

1. Trade Routes: These are defined methods of transportation used by merchants to move goods from one place to another. Throughout history, spice merchants created extensive trade routes to facilitate the movement of spices like pepper, cinnamon, and nutmeg, especially from the East Indies to Europe.

2. Scurvies: This term refers to a disease, typically associated with vitamin C deficiency, primarily affecting sailors. It does not fit the context of the sentence discussing navigation and paths.

3. Circumnavigation: This term means traveling all the way around something, particularly the Earth. While it pertains to a journey, it is not specifically about established routes for trade.

Thus, the most appropriate completion of the sentence is "trade routes," as it fits the historical context of sailors following paths established for the purpose of commerce.