2121. What characters can be added here so that each character contains a part of the previous character? a) 勅 -> _ -> _ -> 販 b) 粒 -> _ -> _ -> 肥

a) 勅 -> 加 -> 員 -> 販  

勅  CHOKU - imperial decree

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

員  IN - member

販  HAN - sell

b) 粒 -> 音 -> 明 -> 肥  

粒  RYUU, tsubu - a grain

音  ON, IN, oto, ne - sound

明  MEI, MYOU, aka(rui), a(keru) - bright

肥  HI, koe, ko(yashi), ko(yasu) - manure, fertilizer, grow fat