 Complete the following phrase:  The final gap between Geosan and Gunseon was closed on 1 September 1928, completing the line in its entirety from Wonsan to Hoeryeong. At the same time, the line was split, with the WonsanCheongjin section being named the Hamgyeong Main Line, and the CheongjinHoeryeong section becoming the Cheongjin Line. These lines later played a major role in the 