1835. What character can be added to both of these characters to give other characters? 任_ -> _反

Answer:

任  NIN, maka(seru) - entrust, responsibility

反  HAN, HON, tane, so(ru) - anti-, bend back

Add 貝:任+貝 貝+反 

貝  KAI - shellfish

賃  CHIN - rent, wages, fee

販  HAN - sell