Answer:
a) 案 -> 柱 -> 素 -> 純
案 AN - plan, proposal
柱 CHUU, hashira - pillar, column, pole
素 SO, SU - element, naked, simple
純 JUN - pure
b) 弦 -> 畜 -> 胃 -> 肺
弦 GEN, tsuru - string, bowstring
畜 CHIKU - animal raising, domestic animal
胃 I - stomach
肺 HAI - lung