634. What character can be added to both of these characters to give other characters? 隊_ -> _曽

Answer:

隊  TAI - party, squad, unit

曽  SOU, katsute - overlap

Add 土: 隊+土 土+曽 

土  DO, tsuchi - earth, soil

墜  TSUI - fall to pieces, collapse, demolish

増  ZOU, ma(su), fu(eru), fu(yasu) - increase, rise, raise