Answer:
Both a and b
Explanation:
The main motivation was a) to find a new sea route to Asia, because after the Ottoman Empire took control of Constantinople in 1453, it became harder for Western European countries to trade with Asia through the East, so they began to look for alternatives through the west.
However, b) also became a motivation. Christianity was deeply rooted in political power by the time, and the advancement of Christianity not only made the Church more powerful, but the governments as well.
