( ( When ( ( ( a ( human 's ) ) ( circadian clock ) ) ( is ( working correctly ) ) ) ) ( , ( ( the ( normal rhythms ) ) ( ( adhere ( to ( a ( 24-hour cycle ) ) ) ) . ) ) ) )
(ROOT (S (SBAR (WHADVP (WRB When)) (S (NP (NP (DT a) (NN human) (POS 's)) (NN circadian) (NN clock)) (VP (VBZ is) (VP (VBG working) (ADVP (RB correctly)))))) (, ,) (NP (DT the) (JJ normal) (NNS rhythms)) (VP (VB adhere) (PP (TO to) (NP (DT a) (JJ 24-hour) (NN cycle)))) (. .)))
When a human's circadian clock is working correctly, the normal rhythms adhere to a 24-hour cycle.
(ROOT (S (NP (NP (JJ Regular) (NNS changes)) (PP (IN in) (NP (NN biology) (CC or) (NN behavior))) (SBAR (WHNP (WDT that)) (S (VP (VBP occur) (PP (IN in) (NP (DT a) (CD 24) (NN hour) (NN cycle))))))) (VP (VBP are) (NP (NP (NN part)) (PP (IN of) (NP (DT the) (NN circadian) (NN rhythm))))) (. .)))