( ( ( ( Metal bond ) , ) ( hydrogen bond ) ) . )
(ROOT (NP (NP (NN Metal) (NN bond)) (, ,) (NP (NN hydrogen) (NN bond)) (. .)))
Metal bond, hydrogen bond.
(ROOT (S (NP (DT The) (JJ metallic) (NN bond)) (VP (VBZ is) (ADJP (JJ responsible) (PP (IN for) (NP (NP (DT the) (NNS properties)) (PP (IN of) (NP (NNS metals))))))) (. .)))