Answer:
a) 動 -> 加 -> 吐 -> 堀
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
堀 hori - moat, canal, ditch
b) 駐 -> 素 -> 紹 -> 超
駐 CHUU - stop, reside
素 SO, SU - element, naked, simple
紹 SHOU - introduction
超 CHOU, ko(su), ko(eru) - cross, go over, exceed