2687. What characters can be added here so that each character contains a part of the previous character? a )炎 -> _ -> _ -> 臓 b) 知 -> _ -> _ -> 惑

a) 炎 -> 畑 -> 胃 -> 臓  

炎  EN, honou - flame

畑  hatake - cultivated field

胃  I - stomach

臓  ZOU - internal organ

b) 知 -> 吐 -> 域 -> 惑  

知  CHI, shi(ru) - know

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

域  IKI - region, area

惑  WAKU, mado(u) - go astray, be tempted