( ( ( ( ( Liquids ( , ( obviously ( , ( ( do not ) ( retain ( a ( fixed shape ) ) ) ) ) ) ) ) , ) but ) ( they ( do ( have ( a ( definite volume ) ) ) ) ) ) . )
(ROOT (S (S (NP (NNS Liquids)) (, ,) (ADVP (RB obviously)) (, ,) (VP (VBP do) (RB not) (VP (VB retain) (NP (DT a) (VBN fixed) (NN shape))))) (, ,) (CC but) (S (NP (PRP they)) (VP (VBP do) (VP (VB have) (NP (DT a) (JJ definite) (NN volume))))) (. .)))
Liquids, obviously, do not retain a fixed shape, but they do have a definite volume.
(ROOT (S (NP (NN Liquid)) (VP (VBZ has) (NP (NP (DT a) (JJ definite) (NN volume)) (, ,) (CONJP (CC but) (RB not)) (NP (DT a) (JJ definite) (NN shape)))) (. .)))