"This is at a time when we are working to relaunch negotiations and we believe that these actions make it more difficult for our efforts to succeed.

VOA: standard.2009.11.17

I want to finish this discussion by including the anti-bonding orbital, and this is a tip for you when you're drawing your molecular orbital diagrams, any time you draw a bonding orbital, there is also an anti-bonding orbital that exists.

我想要以包含反键轨道,来结束这个讨论，告诉你们一个,画分子轨道图的小技巧，任何时候你画一个成键轨道，都会存在一个反键轨道。

麻省理工公开课 - 化学原理课程节选

And this is a picture from emersion week-- emersion week is when the very first time students meet together that for 5 days to Penn.

这是一张开学周的照片-,开学周时，同学初次见面,他们来宾州五天。

哈佛公开课 - 幸福课课程节选

This latest incident comes at a time when Afghanistan is witnessing its worst violence of the eight-year-long war following the ouster of the Taliban from power in 2001.

VOA: standard.2009.09.12

President Zardari has been harshly criticized by some within the Pakistani community in Britain, as well as from back home, for taking this trip - especially at a time when Pakistan is experiencing the worst flooding in decades.

VOA: standard.2010.08.06

Three times in recent weeks, Republicans have used parliamentary tactics in the Senate to block the extension of benefits, angering the president at a time when he is trying to move this and other legislation through Congress before the congressional recess.

VOA: standard.2010.07.19