( ( ( ( ( An atom ) , ) ( ( the ( smallest unit ) ) ( of matter ) ) ) , ) ( ( is ( composed ( of ( ( ( a nucleus ) and ) ( electrons ( which ( orbit ( that nucleus ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NP (DT An) (NN atom)) (, ,) (NP (NP (DT the) (JJS smallest) (NN unit)) (PP (IN of) (NP (NN matter)))) (, ,)) (VP (VBZ is) (VP (VBN composed) (PP (IN of) (NP (NP (DT a) (NN nucleus)) (CC and) (NP (NP (NNS electrons)) (SBAR (WHNP (WDT which)) (S (VP (VB orbit) (NP (DT that) (NN nucleus)))))))))) (. .)))
An atom, the smallest unit of matter, is composed of a nucleus and electrons which orbit that nucleus.
(ROOT (S (NP (DT A) (PRN (-LRB- -LRB-) (NP (NN n)) (-RRB- -RRB-)) (NN atom)) (VP (VBZ is) (NP (NP (DT the) (JJS smallest) (CC and) (JJS most)) (JJ fundamental) (NN unit) (PP (IN of) (NP (NN matter)))) (, ,) (S (VP (VBG consisting) (PP (IN of) (NP (NP (DT a) (NN nucleus)) (VP (VBN surrounded) (PP (IN by) (NP (NNS electrons))))))))) (. .)))