Answer: The Printing Press
Explanation: Gutenberg made way for books to be copied mechanically, and not by hand, allowing books to become widespread for the first time.
I believe the answer would be 1/3.
Answer:
The Equal protection clause.
Explanation:
The doctrine of separate but igual is unconstituional.
Marbury v Madison helped as a background for this case, since the Supremacy Clause of Article VI is the supreme law for the whole land.