(Sound) Twenty years ago, thousands of students braved riot police in Prague, demanding an end to decades of communist rule in what was then Czechoslovakia.

VOA: standard.2009.11.17

So, we see is when we use the octet rule to look at fluorine molecule, we're combining two fluorine atoms, and what we end up with is an f f molecule where they're sharing two electrons, so making that covalent bond.

那么，我们看到把八隅体规则用到氟分子上,就是把两个氟原子组合起来，最终得到的氟分子中两个原子,共用一对电子，这就构成了共价键。

麻省理工公开课 - 化学原理课程节选

Okay, so the rule for adding the two vectors is, you draw the first one and at the end of that first one, you begin the second one.

矢量的加法法则就是,先画出第一个矢量,然后在它的终点,再画第二个矢量

耶鲁公开课 - 基础物理课程节选

He called on a new generation of Africans to build democracy, create opportunity,fight corruption, and end the long cycle of strongman rule and conflict on the continent.

VOA: standard.2009.07.11

The offer came after opposition leader and former prime minister Nawaz Sharif asked for an end to executive rule in Punjab, the dropping of the judicial ruling that banned he and his brother from holding elected office and the restoration of an independent judiciary.

VOA: standard.2009.03.13