(S (S (PP (IN Among) (NP (BASENP (NNS adolescents)) (SBAR (WHNP (WP who)) (S (VP (VBP engage) (PP (IN in) (BASENP (ADJP (JJ oral) (CC or) (JJ vaginal)) (NN sex)))))))) (COMMA ,) (S (NP (BASENP (NNS boys)) (SBAR (WHNP (WP who)) (S (VBP masturbate)))) (VP (VBD were) (ADJP (ADJP (ADJP (QP (NN eight) (NNS times)) (ADJP (RBR more) (JJ likely))) (S (VP (TO to) (VP (VB use) (BASENP (DT a) (NN condom)))))) (PP (IN than) (NP (BASENP (NNS boys)) (SBAR (WHNP (WP who)) (S (VP (VBP do) (RB n't)))))))))) (PERIOD .))