( ( ( Hydrogen and ) oxygen ) ( ( ( ( are elements ) , ) ( because ( they ( each ( contain ( ( only ( one kind ) ) ( of atom ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NN Hydrogen) (CC and) (NN oxygen)) (VP (VBP are) (NP (NNS elements)) (, ,) (SBAR (IN because) (S (NP (PRP they)) (DT each) (VP (VBP contain) (NP (NP (RB only) (CD one) (NN kind)) (PP (IN of) (NP (NN atom)))))))) (. .)))
Hydrogen and oxygen are elements, because they each contain only one kind of atom.
(ROOT (S (NP (PRP You)) (VP (VBP call) (NP (NP (NNS elements)) (SBAR (WHNP (WDT that)) (S (VP (VBP contain) (NP (NP (JJ only) (NNS atoms)) (PP (IN of) (NP (NP (CD one) (NN type)) (PP (IN of) (NP (NN element) (NN native) (NNS elements))))))))))) (. .)))