2500. What characters can be added here so that each character contains a part of the previous character? a) 菓 -> _ -> _ -> 腰 b) 菓 -> _ -> _ -> 堤

a) 菓 -> 柱 -> 青 -> 腰  

菓  KA - cake, fruit

柱  CHUU, hashira - pillar, column, pole

青  SEI, SHOU, ao(i) - blue

腰  YOU, koshi - pelvis, loins, hips, back

b) 菓 -> 棋 -> 基 -> 堤  

菓  KA - cake, fruit

棋  KI - go, shogi, Japanese chess

基  KI, moto, motoi - basis, foundation

堤  TEI, tsutsumi - bank, embankment, dike