Mayoral races in Seoul, Busan, Ulsan and South Gyeongsang Province

South Korea's June 3 election race is heating up, with opinion polls hinting at closer-than-expected races in many key battlegrounds eyed by the ruling Democrat

Exactly a year after people across Korea voted for a new president on June 3 of last year, another nationwide election will take place next week, serving as the first litmus test…