VOA慢速英语:A Sad Day, at an Uneasy Time, as US Marks 9-11 Attacks

center on重点在于…; 主要与…有关

例句：All his attention has centered on that experiment.
      他的全部注意力都集中在那个实验上。

      He centered his attention on the problem.
      他把注意力集中在这个问题上。

2.In reaction, Mr. Jones said he was not canceling the burning, but was suspending it.

not but不是，而是

由but构成的几个常用结构

but for “多亏…” “要不是” 多用于虚拟语气

But for your help,I wouldn’t have succeed. 要是没有你的帮忙，我就不会成功。

not…but “不是…而是…”

I meant not he but you should pay attention to pronunciation.

我说不是他而是你要注意发音。

not only…but also “不但…而且…”

Not only he but also I am interested in pop music. 不但他而且我也对流行歌曲感兴趣。

该结构可以并列任何两个句子成分，在并列两个主语时，要注意谓语动词与就近的主语一致。

cannot help but “不得不”，后接动词原形

We cannot help but admit that the Chinese people are a great people.

我们不得不承认,中华民族是一个伟大的民族.

3.A Muslim student leader at George Washington University, for example, called on Muslim students to take part in a day of community service.

call on叫, 号召

例句：The government called on the workers to oppose waste.
      政府号召工人反对浪费。

4.The Constitution guarantees free speech and bars the government from restricting the practice of religion.

bar from禁止(接近〔做〕…)

例句：The members voted to bar women from the club.
      会员表决不让妇女加入该俱乐部。

      After the member was caught cheating, he was barred from the club.
      那会员行骗被抓后, 被开除会籍。