2542. What characters can be added here so that each character contains a part of the previous character? a) 案 -> _ -> _ -> 紙 b) 劣 -> _ -> _ -> 坪

a) 案 -> 柱 -> 素 -> 紙  

案  AN - plan, proposal

柱  CHUU, hashira - pillar, column, pole

素  SO, SU - element, naked, simple

紙  SHI, kami - paper

b) 劣 -> 加 -> 吐 -> 坪  

劣  RETSU, oto(ru) - be inferior

加  KA, kuwa(eru), kuwa(waru) - add, append, join, take part

吐  TOU, ha(ku) - spew, vomit, give vent to

坪  tsubo - unit of area