( ( ( The higher ) ( the density ) ) ( , ( ( ( the more ) ( closely ( packed ( ( ( the particles ) ( -LRB- ( ( called ( ( atoms and ) molecules ) ) -RRB- ) ) ) are ) ) ) ) . ) ) )
(ROOT (X (X (X (DT The) (JJR higher)) (NP (DT the) (NN density))) (, ,) (X (X (DT the) (JJR more)) (ADJP (RB closely) (SBAR (S (VP (VBD packed) (SBAR (S (NP (NP (DT the) (NNS particles)) (PRN (-LRB- -LRB-) (VP (VBN called) (NP (NNS atoms) (CC and) (NNS molecules))) (-RRB- -RRB-))) (VP (VBP are))))))))) (. .)))
The higher the density, the more closely packed the particles (called atoms and molecules) are.
(ROOT (S (NP (NP (NNP Density)) (PP (IN of) (NP (NN matter)))) (VP (VBZ reflects) (SBAR (WHADVP (WRB how) (RB closely)) (S (VP (VBD packed) (SBAR (S (NP (NP (DT the) (NNS particles)) (PP (IN of) (NP (NN matter)))) (VP (VBP are)))))))) (. .)))