World leaders agreed this week to protect all nuclear materials within four years to stop the possibility of nuclear terrorism.

VOA: special.2010.04.17

So this is a thing, Week Number Four, saw very commonly, which was -- this is something we saw commonly and there's a couple of issues here.

所以这是一件事，第四个，一般的分解，那是我们讲解的东西,这里有好几个问题。

哈佛公开课 - 计算机科学课程节选

This is the end of week four.

这个第四周最后一次课。

哈佛公开课 - 计算机科学课程节选

Forty-four percent in a USA Today/Gallup Poll released this week approved of Barack Obama's handling of the issue.

VOA: special.2009.07.25

This week,we visit four Web sites where students can learn about higher education in the United States.

VOA: special.2009.02.26

"Four of the expelled NGOs have taken advantage of this latter flexibility and this week completed initial registration processes in Khartoum,".

VOA: standard.2009.06.11