( ( For ( ( a current ) ( to flow ) ) ) ( , ( there ( ( must ( be ( ( ( ( ( ( a circuit ) , ) ( ( an ( unbroken loop ) ) ( for ( the ( charge ( to follow ) ) ) ) ) ) , ) and ) ( a ( driving force ) ) ) ) ) . ) ) ) )
(ROOT (S (PP (IN For) (NP (NP (DT a) (NN current)) (PP (TO to) (NP (NN flow))))) (, ,) (NP (EX there)) (VP (MD must) (VP (VB be) (NP (NP (DT a) (NN circuit)) (, ,) (NP (NP (DT an) (JJ unbroken) (NN loop)) (PP (IN for) (NP (DT the) (NN charge) (S (VP (TO to) (VP (VB follow))))))) (, ,) (CC and) (NP (DT a) (VBG driving) (NN force))))) (. .)))
For a current to flow, there must be a circuit, an unbroken loop for the charge to follow, and a driving force.
(ROOT (S (SBAR (IN Because) (S (NP (NNS charges)) (VP (MD must) (VP (VB have) (NP (DT an) (JJ unbroken) (NN path) (S (VP (TO to) (VP (VB follow))))))))) (, ,) (NP (JJ electric) (NN current)) (VP (MD can) (RB not) (VP (VB flow) (PP (IN through) (NP (DT a) (NN material))) (SBAR (IN unless) (S (NP (PRP it)) (VP (VBZ forms) (NP (DT a) (VBN closed) (NN loop))))))) (. .)))