How did the work of Heinrich Schliemann transform our understanding of early Greek civilization?

How did the work of Heinrich Schliemann transform our understanding of early Greek civilization?

a. He found the Cretan Minoan civilization.

b. He proved it was much less sophisticated than previously thought.

c. He showed that Mycenae was destroyed by war.

d. He showed that the Iliad and Odyssey were based on a historical past.