2169. What characters can be added here so that each character contains a part of the previous character? a) 針 -> _ -> _ -> 含 b) 柔 -> _ -> _ -> 結

a) 針 -> 古 -> 吟 -> 含  

針  SHIN, hari - needle

古  KO, furu(i) - old

吟  GIN - sing, chant, recite

含  GAN, fuku(mu), fuku(meru) - hold, include, contain

b) 柔 -> 柱 -> 素 -> 結  

柔  JUU, NYUU, yawa(rakai) - soft

柱  CHUU, hashira - pillar, column, pole

素  SO, SU - element, naked, simple

結  KETSU, musu(bu), yu(u) - tie up, bind