Simplify the following text for a Grade 7 native English-speaking person.
Original: Barnes & Noble , Inc. is the largest book retailer in the United States , operating mainly through its Barnes & Noble Booksellers chain of bookstores headquartered in lower Fifth Avenue in Lower Manhattan , New York City .
Simplified: Barnes & Noble , Inc. is the largest seller of books in the United States . It operates mostly through its Barnes & Noble Booksellers chain of bookstores which is based in lower Fifth Avenue in Lower Manhattan , New York City .