( ( ( ( ( ( The pupil ) ( is ( ( the ( black ( circular hole ) ) ) ( in ( ( the center ) ( of ( the iris ) ) ) ) ) ) ) , ) and ) ( it ( lets ( light ( enter ( the eye ) ) ) ) ) ) . )
(ROOT (S (S (NP (DT The) (NN pupil)) (VP (VBZ is) (NP (NP (DT the) (JJ black) (JJ circular) (NN hole)) (PP (IN in) (NP (NP (DT the) (NN center)) (PP (IN of) (NP (DT the) (NNS iris)))))))) (, ,) (CC and) (S (NP (PRP it)) (VP (VBZ lets) (S (NP (NN light)) (VP (VB enter) (NP (DT the) (NN eye)))))) (. .)))
The pupil is the black circular hole in the center of the iris, and it lets light enter the eye.
(ROOT (S (NP (DT The) (NN pupil)) (VP (VBZ is) (NP (NP (DT the) (NN name)) (PP (IN of) (NP (NP (DT the) (JJ black) (NN opening)) (PP (IN in) (NP (NP (DT the) (NN eye)) (SBAR (WHNP (WDT that)) (S (VP (VBZ lets) (SBAR (S (NP (NN light)) (VP (VBP enter))))))))))))) (. .)))