What Led Portuguese Traders to Explore the Coast of Africa

What led Portuguese traders to explore the coast of Africa in the mid-sixteenth century?

A) Gold's value rose dramatically during and after the Black Death, and the Portuguese believed that Africa was a source of precious metals.
B) The Spanish had taken control of the gold coming from the Americas, so the Portuguese had to look elsewhere.
C) The Portuguese were denied access to the Mediterranean trade in gold by their rivals, the Dutch.
D) The Holy Roman Empire refused to allow the Portuguese merchants a share of trade in gold mined in the Carpathian Mountains.