( ( ( The ( favorable adaptation ) ) ( of ( the crab ) ) ) ( is ... ) )
(ROOT (S (NP (NP (DT The) (JJ favorable) (NN adaptation)) (PP (IN of) (NP (DT the) (NN crab)))) (VP (VBZ is)) (: ...)))
The favorable adaptation of the crab is...
(ROOT (S (NP (NP (DT A) (-LRB- -LRB-) (NN n) (-RRB- -RRB-)) (NP (JJ favorable) (NN trait))) (VP (VBZ is) (NP (DT an) (NN adaptation))) (. .)))
A(n) favorable trait is an adaptation.