( ( The lens ) ( ( may ( be ( ( convex or ) concave ) ) ) . ) )
(ROOT (S (NP (DT The) (NN lens)) (VP (MD may) (VP (VB be) (ADJP (JJ convex) (CC or) (JJ concave)))) (. .)))
The lens may be convex or concave.
(ROOT (S (NP (NP (DT The) (NN lens)) (PP (IN of) (NP (DT the) (NN eye)))) (VP (VBZ is) (S (NP (DT a) (-LRB- -LRB-) (NN n) (-RRB- -RRB-) (NN convex)) (VP (VB shape)))) (. .)))