( ( ( ( ( Discuss ( organic compounds ) ) , ) briefly ) ( describing ( ( the ( four classes ) ) ( of macromolecules ) ) ) ) . )
(ROOT (NP (NP (NP (NNS Discuss)) (NP (JJ organic) (NNS compounds)) (, ,) (ADVP (NN briefly))) (VP (VBG describing) (NP (NP (DT the) (CD four) (NNS classes)) (PP (IN of) (NP (NNS macromolecules))))) (. .)))
Discuss organic compounds, briefly describing the four classes of macromolecules.
(ROOT (S (NP (EX There)) (VP (VBP are) (NP (NP (CD four) (NNS classes)) (PP (IN of) (NP (JJ biochemical) (NNS compounds))))) (. .)))