1. the jeogori has many such curves in the collar, the bottom of the sleeves, the hem, and the front opening, all of (them) are sometimes highlighted with dark lines.
-which가 정답이라는데 이유좀 가르쳐주세요ㅠㅠ;;;

2. for many generations, koreans have long (known) to prefer white-colored clothing.
-been known이라는데 이유가 수동이라서인가요..?

3. white clothing (seem) to contrast well with black hair.
-seems라는데 왜 white clothing이 복수주어가 되었나요..? 포괄적인가?

4. they also say that the contrast suits koreans because their hair and skin tones differ so (great)
-greatly로 바꿔야하는 이유좀 가르쳐주세요ㅠㅠㅠㅠ