(S (S (NP (BASENP (DT A) (ADJP (RB recently) (VBN published)) (JJ nationwide) (NN survey)) (PP (IN of) (BASENP (NNP US) (NNS teenagers)))) (VP (VBZ indicates) (SBAR (S (BASENP (NNS boys)) (VP (VBP tend) (S (VP (TO to) (VP (VB masturbate) (ADVP (ADVP (ADVP (RBR more)) (PRN (COLON --) (VP (CC and) (VP (VB start) (ADVP (RB younger)))) (COLON --))) (PP (IN than) (BASENP (NNS girls)))))))))))) (PERIOD .))