Answer:
a) 駐 -> 素 -> 紡 -> 放
駐 CHUU - stop, reside
素 SO, SU - element, naked, simple
紡 BOU, tsumu(gu) - spin, make yarn
放 HOU, hana(reru), hana(tsu), hana(su) - to let loose, release, emit
b) 弦 -> 畜 -> 胃 -> 胎
弦 GEN, tsuru - string, bowstring
畜 CHIKU - animal raising, domestic animal
胃 I - stomach
胎 TAI - womb, uterus