( ( For ( four triangles ) ) ( , ( we ( ( can ( ( form ( a ( cup shape ) ) ) ( by ( ( pushing ( ( one vertex ) ( of ( the octahedron ) ) ) ) in ) ) ) ) . ) ) ) )
(ROOT (S (PP (IN For) (NP (CD four) (NNS triangles))) (, ,) (NP (PRP we)) (VP (MD can) (VP (VB form) (NP (DT a) (NN cup) (NN shape)) (PP (IN by) (S (VP (VBG pushing) (NP (NP (CD one) (NN vertex)) (PP (IN of) (NP (DT the) (NN octahedron)))) (PP (IN in))))))) (. .)))
For four triangles, we can form a cup shape by pushing one vertex of the octahedron in.
(ROOT (S (NP (NP (DT The) (CD eight) (NNS sides)) (PP (IN of) (NP (DT an) (NN octahedra)))) (VP (VBP are) (PP (IN in) (NP (NP (DT the) (NN shape)) (PP (IN of) (NP (DT a) (NNS triangles)))))) (. .)))