Douglas-Cooper, H. (1999). As 70 maravilhas do mundo moderno. Selecções do Reader's Digest.
শিকাগো স্টাইল (17 তম সংস্করণ) উদ্ধৃতিDouglas-Cooper, Helen. As 70 Maravilhas Do Mundo Moderno. Selecções do Reader's Digest, 1999.
M.L.A (8 ম সংস্করণ) উদ্ধৃতিDouglas-Cooper, Helen. As 70 Maravilhas Do Mundo Moderno. Selecções do Reader's Digest, 1999.
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