( Students ( ( combine ( ( simple machines ) ( to ( build ( ( a ( unique ( compound machine ) ) ) ( of ( their ( own design ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NNS Students)) (VP (VBP combine) (S (NP (JJ simple) (NNS machines)) (VP (TO to) (VP (VB build) (NP (NP (DT a) (JJ unique) (NN compound) (NN machine)) (PP (IN of) (NP (PRP$ their) (JJ own) (NN design)))))))) (. .)))
Students combine simple machines to build a unique compound machine of their own design.
(ROOT (S (NP (NNS Scissors)) (VP (VBP are) (NP (JJ compound) (NNS machines))) (. .)))