2521. What characters can be added here so that each character contains a part of the previous character? a) 動 -> _ -> _ -> 幸 b) 章 -> _ -> _ -> 珠

a) 動 -> 加 -> 吐 -> 幸  

動  DOU , ugo(ku) - move

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

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

幸  KOU, shiawa(se), sachi - happiness, good fortune

b) 章 -> 古 -> 呈 -> 珠  

章  SHOU - chapter, badge, mark

古  KO, furu(i) - old

呈  TEI - offer, present, exhibit

珠  SHU - pearl