2094. What characters can be added here so that each character contains a part of the previous character? a) 案 -> _ -> _ -> 砂 b) 篤 -> _ -> _ -> 結

a) 案 -> 棋 -> 碁 -> 砂  

案  AN - plan, proposal

棋  KI - go, shogi, Japanese chess

碁  GO - go (board game)

砂  SA, SHA, suna - sand

b) 篤 -> 駐 -> 素 -> 結  

篤  TOKU - serious, cordial

駐  CHUU - stop, reside

素  SO, SU - element, naked, simple

結  KETSU, musu(bu), yu(u) - tie up, bind