Answer:
C. Knossos
Step-by-step explanation:
Knossos has been known as the oldest city of Europe. It is located on the island of Crete in Mediterranean sea and is the largest archaeological site of Bronze age.
It is also the place where Minoan civilization flourished between 2700 to 1450 BC. Minoan civilization was a Bronze age civilization which is represented as the first advanced civilization of Europe as it is known for it's writing system, building complexes, tools, excellent artwork and most importantly it's massive network of trade especially from Athenians.
So, if Athenians wanted to trade with Minoan then they have to travel to city of Knossos.