Answer: C. Europeans began to search for a water-based trade route to Asia.
Step-by-step explanation:
Before the Ottomans conquered Constantinople, the Europeans used it to access Asia via the Silk Road. With the conquest of the city, Europeans did not want to go through Muslim Ottoman held territories and so had to find a water-based route to Asia to continue trade.
This was accomplished in 1499 when Vasco da Gama reached India via the ocean and heralded a new age in sea exploration.