( People ( ( can ( ( live ( for weeks ) ) ( ( ( ( ( without food ) , ) but ) only ) ( ( a ( few days ) ) ( without water ) ) ) ) ) . ) )
(ROOT (S (NP (NNS People)) (VP (MD can) (VP (VB live) (PP (IN for) (NP (NNS weeks))) (PP (PP (IN without) (NP (NN food))) (, ,) (CC but) (RB only) (PP (NP (DT a) (JJ few) (NNS days)) (IN without) (NP (NN water)))))) (. .)))
People can live for weeks  without food, but only a few days without water.
(ROOT (S (NP (JJS Most) (NNS people)) (VP (MD can) (VP (VB survive) (NP (QP (RB only) (DT a) (JJ few)) (NNS days)) (PP (IN without) (NP (NN water))))) (. .)))