( ( ( Only ( hydrogen lines ) ) ( because hydrogen ) ) ( ( is ( ( the ( ( most common ) element ) ) ( in ( the Universe ) ) ) ) . ) )
(ROOT (S (NP (NP (RB Only) (NN hydrogen) (NNS lines)) (PP (IN because) (NP (NN hydrogen)))) (VP (VBZ is) (NP (NP (DT the) (ADJP (RBS most) (JJ common)) (NN element)) (PP (IN in) (NP (DT the) (NNP Universe))))) (. .)))
Only hydrogen lines because hydrogen is the most common element in the Universe.
(ROOT (S (NP (DT The) (NN sun)) (ADVP (RB mostly)) (VP (VBD made) (PRT (RP up)) (PP (IN of) (NP (DT the) (NN element) (NN hydrogen)))) (. .)))