( ( ( ( Grinding and ) polishing ) ( the mirror ) ) ( ( is ( ( the ( ( most difficult ) part ) ) ( of ( making ( a telescope ) ) ) ) ) . ) )
(ROOT (S (S (VP (VBG Grinding) (CC and) (VBG polishing) (NP (DT the) (NN mirror)))) (VP (VBZ is) (NP (NP (DT the) (ADJP (RBS most) (JJ difficult)) (NN part)) (PP (IN of) (S (VP (VBG making) (NP (DT a) (NN telescope))))))) (. .)))
Grinding and polishing the mirror is the most difficult part of making a telescope.
(ROOT (S (NP (NN Ground) (NN tissue)) (VP (VBZ makes) (PRT (RP up)) (NP (NP (JJS most)) (PP (IN of) (NP (NP (DT the) (NN inside)) (PP (IN of) (NP (DT a) (NN plant))))))) (. .)))