A third of the Senate and the entire House are up for re-election.

1/3的参议员和全体众议员将重新选举。

《柯林斯英汉双解大词典》

Every member of the House of Representatives and about one-third of the Senate is up for reelection in any given election year.

在每个规定的选举年中，全国都要重新选举全体的众议院议员和大约三分之一的参议院议员。

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Leading the FDP into a federal election for the third time, Mr Westerwelle accepts much of this.

这已是威氏第三次带领自民党参与联邦大选，他接受大部分罗氏提出的意见。

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For further exploration of my reasoning on this, see my answer to Who are the (compelling) third party candidates for the 2012 US Presidential Election? and my answer to After the economy, what is the single most important issue for the American electorate in the 2012 Presidential Race?

FORBES: Should I Vote For Barack Obama Or Mitt Romney And Why?

Another case that may go before the court concerns three Constitutional Court magistrates sacked after they ruled in 1997 that Mr Fujimori could not run for a third term in the election due next April.

ECONOMIST: Peru

The Tories had promised before the general election to keep the funds for the poorest third of families and for parents with disabled children, but are now going back on this promise, he told MPs.

BBC: Savings Accounts and Health in Pregnancy Bill part 1