VOA慢速英语:Early Classes = Sleepy Teens (Duh!)

an average of平均有(跟数词)

例句：An average of two students are absent each day.
      每天平均有两个学生缺席。

2.In the end, schools ought to do what's the right thing for their students, first and foremost.

first and foremost首要的

例句：He was a singer, but first and foremost a scholar.
      他是个歌手, 但他主要是一位学者。

ought to和should的区别

(1)一般说来，两者可替换，只是ought to语气稍重。如：

You ought to [should] go and see Mary sometime. 你应该什么时候去看看玛丽。

The train ought to [should] have arrived at six. 火车本应该6点钟到的。　

(2)表示出于法令规则、行为准则、道德责任等客观情况而“应该”做某事时，一般应用ought to，若用should则含有个人意见，强调主观看法。如：

(We ought to go and see Mary tomorrow, but I don’t think we will. 明天我们按理应该去看看玛丽，但是我认为我们不会去(此句不宜用should)。

(3)在公告、须知或条例中，出于礼貌，常用should。如：
You should not run alongside the swimming-pool. 不准在游泳池边奔跑。

3.And then going to school I'm out of it, and through first and second period I can barely stay awake.

rarely, seldom,hardly,scarcely, barely 的用法和区别

rarely,很少地，难得地，少见地
　　seldom,表示频率，很少，不常，反义词often
　　hardly 几乎不，简直不= almost not ,强调困难
　　scarcely = hardly 几乎不，简直没有，仅仅，刚刚,用在be/助动词后，强调数量和程度的不足
　　barely 仅仅，刚刚，几乎不能，强调勉强够数

4.These aren't a bunch of lazy kids -- although, you know, teenagers can of course be lazy.

a bunch of许多，一群

例句：They are a bunch of nuts.
      他们是一群疯子。

5.He wanted to see if a thirty-minute delay would make a difference.

make a difference紧要，有影响，起作用

例句：Will the rice I donate make a difference?
      我捐的大米管用吗？