Context: In the early part of the 20th century, Atlantic City went through a radical building boom. Many of the modest boarding houses that dotted the boardwalk were replaced with large hotels. Two of the city's most distinctive hotels were the Marlborough-Blenheim Hotel and the Traymore Hotel.

Question: When did Atlantic City go through a radical building boom?
Answer: early part of the 20th century

Question: What replaced many of the modest boarding houses? 
Answer: large hotels

Question: What were the names of two of the city's most distinctive hotels?
Answer: Marlborough-Blenheim Hotel and the Traymore Hotel

Question: What happened to Atlantic City in the early part of the 20th century?
Answer: a radical building boom

Question: Where were the modest boarding houses located before they were replaced by large hotels?
Answer: the boardwalk