( ( Answer ( If ( you ( ( have ever ) ( looked ( at ( ( the lens ) ( of ( a ( magnifying glass ) ) ) ) ) ) ) ) ) ) ( , ( you ( ( know ( it ( ( ( is ( thick ( in ( the middle ) ) ) ) and ) ( ( tapers ( to nothing ) ) ( at ( the edges ) ) ) ) ) ) . ) ) ) )
(ROOT (S (SBAR (NP (NNP Answer)) (IN If) (S (NP (PRP you)) (VP (VBP have) (ADVP (RB ever)) (VP (VBN looked) (PP (IN at) (NP (NP (DT the) (NN lens)) (PP (IN of) (NP (DT a) (VBG magnifying) (NN glass))))))))) (, ,) (NP (PRP you)) (VP (VBP know) (SBAR (S (NP (PRP it)) (VP (VP (VBZ is) (ADJP (JJ thick) (PP (IN in) (NP (DT the) (NN middle))))) (CC and) (VP (VBZ tapers) (PP (TO to) (NP (NN nothing))) (PP (IN at) (NP (DT the) (NNS edges)))))))) (. .)))
Answer If you have ever looked at the lens of a magnifying glass, you know it is thick in the middle and tapers to nothing at the edges.
(ROOT (S (NP (DT A) (JJ concave) (NN lens)) (VP (VBZ is) (NP (NP (JJR thicker)) (PP (IN at) (NP (DT the) (NNS edges)))) (SBAR (IN than) (S (NP (PRP it)) (VP (VBZ is) (PP (IN in) (NP (DT the) (NN middle))))))) (. .)))
A concave lens is thicker at the edges than it is in the middle.