A Complex Vowel is made up of two simple vowels.
1. y+simple vowel
ㅑ- ya
ㅕ- yeo
ㅛ - yo
ㅠ - yu
ㅒ- yae
ㅖ- ye
2. w+simple vowel and oe and ui
와 - wa
외 - oe
왜 - wae
워 - wo
위 - wi
웨 - we
의 - ui
