( Carbon ( always ( ( forms ( ( ( ( ( ( ( ( ( ( four bonds ) ( as ( either ( four ( single bonds ) ) ) ) ) , ) or ) ( ( ( two ( single bonds ) ) and ) ( one ( double bond ) ) ) ) , ) or ) ( one ( single bond ) ) ) and ) ( ( ( ( ( one ( triple bond ) ) , ) or ) occasionally ) ( two ( double bonds ) ) ) ) ) . ) ) )
(ROOT (S (NP (NNP Carbon)) (ADVP (RB always)) (VP (VBZ forms) (NP (NP (NP (CD four) (NNS bonds)) (PP (IN as) (NP (DT either) (CD four) (JJ single) (NNS bonds)))) (, ,) (CC or) (NP (NP (CD two) (JJ single) (NNS bonds)) (CC and) (NP (CD one) (JJ double) (NN bond))) (, ,) (CC or) (NP (CD one) (JJ single) (NN bond)) (CC and) (NP (NP (CD one) (JJ triple) (NN bond)) (, ,) (CC or) (ADVP (RB occasionally)) (NP (CD two) (JJ double) (NNS bonds))))) (. .)))
Carbon always forms four bonds as either four single bonds, or two single bonds and one double bond, or one single bond and one triple bond, or occasionally two double bonds.
(ROOT (S (NP (DT A) (JJ double) (NN bond)) (VP (VBZ consists) (PP (IN of) (NP (NP (CD one) (NN sigma) (NN bond)) (CC and) (NP (CD one) (NN pi) (NN bond))))) (. .)))