Answer:
a) 切 -> 召 -> 吐 -> 坂
切 SETSU, ki(ru), ki(reru) - cut
召 SHOU, me(su) - summon, wear, take
吐 TOU, ha(ku) - spew, vomit, give vent to
坂 HAN, saka - slope, hill
b) 妙 -> 劣 -> 加 -> 吸
妙 MYOU - strange, odd, adroit, mystery
劣 RETSU, oto(ru) - be inferior
加 KA, kuwa(eru), kuwa(waru) - add, append, join, take part
吸 KYUU, su(u) - suck, inhale, smoke