美国总统大选即将来临
US presidential rivals Barack Obama and Mitt Romney are approaching the final day of their election battle.
美国总统候选人奥巴马与罗姆尼即将迎来大选的最后一天。
Mr Romney is trailing narrowly in key states according to opinion polls
The pair spent Sunday addressing crowds across the country, with Mr Romney speaking in Pennsylvania, a state his aides insist he can now win on Tuesday.
Mr Obama held rallies in New Hampshire and Florida and carried on to Ohio and Colorado in the evening.
Analysts say the election will come down to a handful of swing states.
Mr Obama and Mr Romney are running almost neck-and-neck in national polls, but polls of many key battlegrounds show Mr Obama narrowly ahead.
However, neither camp is exuding（散发，流出） absolute confidence, the BBC's North America editor Mark Mardell reports.
The campaign has been most intense in Ohio, which no Republican has ever lost and still made it to the White House.
Race 'tightening'
A final poll published on Sunday by Ohio's Columbus Dispatch gave Mr Obama a 2% lead - 50% to 48% - over his rival, within the margin of error.
Both candidates visited the Buckeye State on Sunday, with Mr Romney telling crowds in Cleveland that Mr Obama has failed in his pledge to be a "post-partisan" president and criticising his record.
"He's been divisive, blaming, attacking, dividing and - by the way - it's not only Republicans that he refused to listen to, he also refused to listen to independent voices."
Later on Sunday he spoke in Morrisville, Pennsylvania, his first visit there in the final stages of the campaign. Democrats say the Romney team's last-minute decision to campaign in the state is a sign of desperation, but polls do show a tightening race.
"The people of America understand we're taking back the White House because we're going to win Pennsylvania," Mr Romney told the crowd in Morrisville.