Answer:
D. Wooden; steel-based
Explanation:
I am not completely sure, but I think it's letter D.
Andrew Carnegie found a way to develop steel quicker or faster, and therefore steel was not nearly as expensive. Skyscrapers where starting to be built because of it, and cities began to thrive due to the new invention.
Carnegie is from Pittsburgh, Pennsylvania; that's why Pittsburgh is nicknamed as the "Steel City."
Please mark me Brainliest; I need it to move on to the next level! =)
