1. 杉木   oak   poplar   pine   fir   Hint Half-n-half Clue   2. 桦树   maple   birch   beech   pine   Half-n-half Clue   3. 橡木   elm   birch   oak   cedar   Half-n-half Clue   4. 白杨树   poplar   oak   chestnut   elm   Half-n-half Clue   5. 冷杉   maple   fir   poplar   birch   Half-n-half Clue   6. 雪松   beech   birch   pine   cedar   Half-n-half Clue   7. 山毛榉   maple   poplar   beech   elm   Half-n-half Clue