( ( ( ( ( Alternating current ) , ) ( in contrast ) ) , ) ( ( is ( ( electric current ) ( that ( ( reverses ( its ( flow direction ) ) ) ( at ( regular intervals ) ) ) ) ) ) . ) )
(ROOT (S (NP (NP (VBG Alternating) (NN current)) (, ,) (PP (IN in) (NP (NN contrast))) (, ,)) (VP (VBZ is) (NP (NP (JJ electric) (NN current)) (SBAR (WHNP (WDT that)) (S (VP (VBZ reverses) (NP (PRP$ its) (NN flow) (NN direction)) (PP (IN at) (NP (JJ regular) (NNS intervals)))))))) (. .)))
Alternating current, in contrast, is electric current that reverses its flow direction at regular intervals.
(ROOT (S (NP (VBG Alternating) (NN current)) (VP (VBZ is) (NP (NP (DT the) (NN term)) (PP (IN for) (NP (JJ electric) (NN current))) (SBAR (WHNP (WDT that)) (S (VP (VBZ keeps) (S (VP (VBG reversing) (NP (NN direction))))))))) (. .)))