This exercise uses vocabulary that is upper intermediate or above. Still, I'm hoping you can figure it out. If not, look up the words in a dictionary or just scroll down to the vocabulary section, where you'll find the Korean words and their English equivalents. To start, though, make an effort to complete the exercise on your own.
화이팅!
개울 gaeul -- brook
동굴 dong-gul -- cave
바위 bawi -- rock
분화구 bunhwagu -- crater
습지 seubji -- marsh
암초 amcho -- reef
열도 yeoldo -- archipelago
폭포 pogpo -- waterfall
해협 haehyeob -- strait
협곡 hyeobgog -- canyon