( ( ( PUPIL ( The ( adjustable opening ) ) ) ( at ( ( the center ) ( of ( ( the iris ) ( that ( allows ( ( ( varying amounts ) ( of light ) ) ( to ( enter ( the eye ) ) ) ) ) ) ) ) ) ) ) . )
(ROOT (S (VP (VB PUPIL) (NP (DT The) (JJ adjustable) (NN opening)) (PP (IN at) (NP (NP (DT the) (NN center)) (PP (IN of) (NP (NP (DT the) (NNS iris)) (SBAR (WHNP (WDT that)) (S (VP (VBZ allows) (NP (NP (VBG varying) (NNS amounts)) (PP (IN of) (NP (NN light))) (S (VP (TO to) (VP (VB enter) (NP (DT the) (NN eye)))))))))))))) (. .)))
PUPIL The adjustable opening at the center of the iris that allows varying amounts of 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.