( ( ( ( Two-dimensional ( wave propagation ) ) , ) ( surface waves ) ) . )
(ROOT (NP (NP (JJ Two-dimensional) (NN wave) (NN propagation)) (, ,) (NP (NN surface) (NNS waves)) (. .)))
Two-dimensional wave propagation, surface waves.
(ROOT (S (NP (EX There)) (VP (VBP are) (NP (NP (CD two) (NNS types)) (PP (IN of) (NP (NN surface) (NNS waves))))) (. .)))