Final answer:
The early Portuguese explorers primarily aimed to find a sea route to Asia to access the spice trade and spread Christianity, but also engaged in trading gold and participating in the slave trade. so, option b is the correct answer.
Step-by-step explanation:
The main goal of the early Portuguese explorers was to find a water route to Asia. Their exploration was driven by various motivations, including the desire to tap into the lucrative trade with Asia in spices such as cloves, pepper, and ginger. This trade was particularly appealing because it would weaken the Muslim world's control over the spice trade and enrich Portugal financially. Additionally, they held a strong desire to spread Christianity and to establish an alliance with legendary Christian kingdoms to counter the influence of Islam.
The voyages thus were not solely focused on wealth but were also a response to religious and geopolitical interests. The pursuit of gold and the involvement in the slave trade eventually became important aspects of their exploration and colonial activities as they established trading ports and outposts along the coast of Africa.