(S (S (S (VP (TO To) (VP (VB further) (BASENP (PRPD his) (NN research))))) (S (BASENP (NNP Bogaert)) (VP (VBD studied) (BASENP (NN 944) (ADJP (JJ heterosexual) (CC and) (JJ homosexual)) (NNS men))))) (PERIOD .))