Complex sentence: "HuH" was being used as the promotional song for the mini-album, the song debuted at number 5 on South Korea's Gaon Singles Chart and later peaked at number 3 for two weeks.
Split into simpler sentences: HuH was being used as the promotional song for the mini-album. The song debuted at number 5 on South Korea's Gaon Singles Chart and later peaked at number 3 for two weeks.