今天我们要学的词是 biennial.

Biennial 的意思是两年一次的。North Korea is no longer South Korea's “enemy,” though Pyongyang's nuclear program still poses a security threat, according to Seoul's biennial defense document published recently. 首尔最近公布的两年一期的国防文件中称，尽管平壤的核计划仍构成安全威胁，但朝鲜不再是韩国的“敌人”。

While the biennial election of all 435 members of the House and one-third of the Senate typically lacks the voter interest compare to a presidential election every four years, last year's midterms were an exception. 相比（美国）四年一次的总统选举，选民们通常对众议院全体435名议员和参议院三分之一议员两年一次的选举缺乏兴趣，但去年的中期选举是个例外。