Final answer:
The main reason for European exploration in the 15th century was the search for a sea route to Asia to obtain luxury goods more effectively. This was due to the high cost and difficulty of transporting goods along the Silk Road as well as religious motivations.
Step-by-step explanation:
In the fifteenth century, a big impetus for European exploration was: b) A sea route to Asia to obtain luxury goods. Europeans needed to find other routes to bring the exotic spices, silk, porcelain, and other imports. This search for a new route was motivated by the high cost and slowness of transporting goods along the Silk Road, which was subject to taxes by Muslim middlemen, and conflicts like the Crusades that made these routes more perilous and costly. Additionally, a strong motive was the religious zeal of nations such as Spain and Portugal, which aimed to spread Christianity and reclaim lands from the Muslims.
Trade with Asia, including China, and seeking alternatives to the heavily-taxed Silk Road were major factors. Furthermore, the discovery of the Americas added pressure on European states to find new sources of wealth and establishing colonies. European powers like Portugal and Spain were eager to establish new maritime trade routes to Asia to bypass Venetian and Ottoman-controlled land routes and to claim new territories and resources.