( Density ( ( is ( defined ( as ( ( the amount ) ( of ( matter ( per ( unit volume ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NNP Density)) (VP (VBZ is) (VP (VBN defined) (PP (IN as) (NP (NP (DT the) (NN amount)) (PP (IN of) (NP (NP (NN matter)) (PP (IN per) (NP (NN unit) (NN volume))))))))) (. .)))
Density is defined as the amount of matter per unit volume.
(ROOT (S (NP (NNP Density)) (VP (VBZ describes) (SBAR (WHADJP (WRB how) (JJ much)) (S (NP (NN matter)) (VP (VBZ is) (PP (IN in) (NP (NP (DT a) (JJ certain) (NN amount)) (PP (IN of) (NP (NN space))))))))) (. .)))