Macao was a
a. trade route.
c. british explorer.
b. port city.
d. chinese delicacy

Macao is a city (in an autonomous region in China today) - so it can't be an explorer or a route or a delicacy - so just knowing that Macao is a city is enough to know that  answer b) is the correct one.

It was a port city where the foreigners could trade with the Chinese.

Answer metamorphic rock;