The four main islands of Japan are Hokkaido, Honshu, Shikoku, and Kyushu. Honshu is the largest and most populous island, containing major cities like Tokyo and Osaka. Options A, C, and D incorrectly substitute major islands with cities (Yokohama, Sapporo) or smaller islands (Chichi, Okinawa - Okinawa is part of the Ryukyu Islands, not one of the four main islands).