2613. What characters can be added here so that each character contains a part of the previous character? a) 要 -> _ -> _ -> 球 b) 案 -> _ -> _ -> 脚

a) 要 -> 如 -> 呈 -> 球  

要  YOU, i(ru) - essential(s) need

如  JO, NYO - equal, like, as, as if

呈  TEI - offer, present, exhibit

球  KYUU, tama - ball, sphere

b) 案 -> 柱 -> 青 -> 脚  

案  AN - plan, proposal

柱  CHUU, hashira - pillar, column, pole

青  SEI, SHOU, ao(i) - blue

脚  KYAKU, KYA, ashi - leg