(S (S (ADVP (RB However)) (COLON ;) (S (SBAR (WHNP (WP what)) (S (VP (VBZ is) (NP (JJ likely) (NP (BASENP (DT the) (ADJP (RBS most) (JJ famous)) (NN event)) (SBAR (WHNP (WP that)) (S (VP (VP (VBD took) (BASENP (NN place))) (PP (IN at) (BASENP (DT the) (NN exposition))))))))))) (VP (VBD was) (NP (NP (BASENP (DT the) (NN assassination)) (PP (IN of) (BASENP (JJ then) (NNP President) (NNP William) (NNP McKinley)))) (PP (IN on) (NP (BASENP (NNP September) (NN 6)) (COMMA ,) (NN 1901))))))) (PERIOD .))