https://books.google.co.kr/books?id=ONhSDwAAQBAJ&printsec=frontcover&dq=inauthor:%22Sarah+Thornton%22&hl=ko&sa=X&redir_esc=y#v=onepage&q&f=false
https://books.google.co.kr/books?id=f0KAAwAAQBAJ&lpg=PP1&hl=ko&pg=PT8#v=onepage&q&f=false
https://books.google.co.kr/books?id=ONhSDwAAQBAJ&printsec=frontcover&dq=inauthor:%22Sarah+Thornton%22&hl=ko&sa=X&redir_esc=y#v=onepage&q&f=false
https://books.google.co.kr/books?id=f0KAAwAAQBAJ&lpg=PP1&hl=ko&pg=PT8#v=onepage&q&f=false
수정한 이유 :