Portugal sought a sea route to Asia in the 1400s because
a.
Spain controlled all the riches in present-day Mexico and South America.
b.
Coronado had returned to Portugal with gold discovered in the Seven Cities of Cíbola.
c.
Venice monopolized Asian trade on the Silk Road and the Mediterranean Sea.
d.
the Treaty of Tordesillas gave Portugal rights to all of Asia.

C.   Venice monopolized Asian trade on the Silk Road and the Mediterranean Sea.

Explanation:

Portuguese sought a sea route to Asia in 1400 because they were not comfortable with how Venice was monopolizing the trades in Asia through the roads in silk and on the Mediterranean sea.

This period was the renaissance period where there was a quest for discovery in culture, and science in Europe. It resulted in conflicts between these European countries because they were struggling to acquire new lands and create more wealth. This was why they seek a new route to Asia making use of the Mediterranean sea via Africa.

C

Explanation:

d. migration