1. air
   1. wind
   2. storm
      1. twister
      2. tornado
      3. cloud
   3. breathe
2. fire
   1. volcano
   2. lightning
   3. sun
      1. hot
   4. burn
3. earth
   1. moutain
      1. summit
         1. climb
      2. rock
         1. stone
      3. hill
   2. plain
      1. field
         1. grass
   3. forest
      1. wood
   4. desert
4. water
   1. salty
      1. sea
         1. wave
            1. pebble
      2. ocean
         1. island
         2. tide
   2. fresh
      1. river
         1. white-water
         2. waterfall
         3. spring
      2. pond
         1. pool
      3. rain
         1. fog
   3. ice
      1. glacier
      2. hail
      3. cold