( ( ( ( ( The pupil ) , ) ( as ( you ( probably know ) ) ) ) , ) ( ( ( is simply ) ( ( ( a ( `` ( hole '' ) ) ) ( in ( ( the middle ) ( of ( the iris ) ) ) ) ) ( that ( allows ( light ( to ( enter ( the eye ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NP (DT The) (NN pupil)) (, ,) (SBAR (IN as) (S (NP (PRP you)) (ADVP (RB probably)) (VP (VBP know)))) (, ,)) (VP (VBZ is) (ADVP (RB simply)) (NP (NP (DT a) (`` ``) (NN hole) ('' '')) (PP (IN in) (NP (NP (DT the) (NN middle)) (PP (IN of) (NP (DT the) (NNS iris))))) (SBAR (WHNP (WDT that)) (S (VP (VBZ allows) (ADJP (JJ light) (S (VP (TO to) (VP (VB enter) (NP (DT the) (NN eye))))))))))) (. .)))
The pupil, as you probably know, is simply a &quot;hole&quot; in the middle of the iris that allows light to enter the eye.
(ROOT (S (NP (NP (DT The) (NN pupil)) (PP (IN of) (NP (DT the) (NN eye)))) (VP (VBZ allows) (ADJP (JJ light) (S (VP (TO to) (VP (VB enter)))))) (. .)))
The pupil of the eye allows light to enter.