( ( A Concussion ) ( ( is ( a ( Brain injury ) ) ) . ) )
(ROOT (S (NP (DT A) (NNP Concussion)) (VP (VBZ is) (NP (DT a) (NNP Brain) (NN injury))) (. .)))
A Concussion is a Brain injury.
(ROOT (S (NP (DT A) (PRN (-LRB- -LRB-) (NP (NN n)) (-RRB- -RRB-)) (NN concussion)) (VP (VBZ is) (NP (NP (DT the) (ADJP (RBS most) (JJ common)) (NN type)) (PP (IN of) (NP (NN brain) (NN injury))))) (. .)))