2458. What characters can be added here so that each character contains a part of the previous character? a) 炉 -> _ -> _ -> 軒 b) 如 -> _ -> _ -> 黒

a)  -> 扉 -> 輩 -> 軒  

炉  RO - furnace, hearth

扉  HI, tobira - door, title page

輩  HAI - fellow, colleague, companion

軒  KEN, noki - counter for buildings, eaves

b) 如 -> 吐 -> 埋 -> 黒  

如  JO, NYO - equal, like, as, as if

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

埋  MAI, u(maru), u(meru), u(moreru) - bury, be buried, filled up

黒  The "Kuro" radical - black