The war of words was intensified as U.S. presidential candidates John McCain and Barack Obama argued about who has a better economic plan in their final debate Wednesday night at Hofstra University, Hempstead, N.Y.

　　McCain asked his Democratic opponent Obama to clarify his relationship with Bill Ayers, a former 1960s radical who belonged to the Weather Underground.

　　"Mr. Ayers is not involved in this campaign, he has never been involved in my campaign, and he will not advise me in the White House," Obama said.

　　McCain's campaign has charged that Obama's association with Ayers should cause voters to question his judgment. Ayers was a founding member of the radical Weather Underground, a group that was involved in bombings in the early 1970s, including attacks on the Pentagon and the Capitol.

　　McCain and Obama went back-and-forth Wednesday over the negative rhetoric that has dominated the campaign trail in recent days.

　　McCain accused Obama of spending "more money on negative ads than any campaign in history." Obama hit back, saying that McCain's campaign had been running exclusively negative ads, and that the public found McCain to be running a more negative campaign than Obama.