( ( there ( were ( ( food and ) oxygen ) ) ) ( , ( both ( ( provided ( by plants ) ) . ) ) ) )
(ROOT (S (S (NP (EX there)) (VP (VBD were) (NP (NN food) (CC and) (NN oxygen)))) (, ,) (NP (DT both)) (VP (VBD provided) (PP (IN by) (NP (NNS plants)))) (. .)))
there were food and oxygen, both provided by plants.
(ROOT (S (NP (NNS Plants)) (VP (CONJP (RB not) (JJ only)) (VP (VBP contribute) (NP (NN food))) (CC but) (VP (VBD oxygen) (PP (IN for) (NP (NNS organisms))))) (. .)))