VOA慢速英语:Breathing Easier: The Art of Stove Making

1.More than three billion people are at risk from indoor air pollution because of the heating or cooking fuels they use.

at risk在危险中,在危急时

例句：The whole future of the company is at risk.
      这家公司的整个前途都处在危险之中。

处于……的风险中，用at risk of，相当于 in danger of

例句：He is at the risk of failing because of his low scores.
      他因为低分而有不合格的危险。
 
2.It's been estimated that wood is running out more quickly than oil and gas.

run out耗尽

例句：The hotel has run out of beer .
      这饭店的啤酒已全部售完了。

类似的词组：

fall short不足,缺乏;达不到,不符合

例句：This month we may fall short of our goals.
      这个月我们可能无法达到我们的目标。

3.The Lorena was very good at reducing smoke and warming homes.

be good at善于,擅长于

例句：The captain is good at helping one be at one's ease.
      队长善于助人稳定心情。

4.The Lorena used twice as much wood as an open fire, and took much longer to heat food.

twice as much倍数的比较

表示三以上的倍数用times，但表示两倍（汉语中的一倍实际上也指两倍）时则用twice, double, duple, twofold, as…again as表示。译为

“翻一番”或“为…的两倍”。3倍常用three times, triple, threefold表示，译为“增加2倍，增至三倍”或“为…的3倍”。4倍用

quadruple，基数词＋times，基数词＋fold表示，译为“增加3倍，增至4倍”或“为…的4倍”。例如：
  He earned double the usual wage in holiday. 他在假期里挣了比平时多1倍的工资。
 This bridge is as long again as that bridge. 这座大桥的长度是那座大桥的2倍。
  They have produced four-fold as many laptops as they did last year.他们今年生产的笔记本电脑相当于去年的4倍。
Their grains have trebled (tripled) this year. 他们的粮食今年增加了2倍（是…的三倍）。

1) 主语+谓语+ X times + as + adj. + as
这个句型译为：① A…是B的X倍（或净增加X－1倍）.
例如：This pen (A) is twice as expensive as that pen (B).
这只钢笔(A)的价格是那只钢笔(B)的2倍。（即A比B贵一倍）
I have three times as many as you.　我有你三倍那么多。（我的比你的多两倍）
 This box is four times as heavy as that box. 这个盒子比那个盒子重4倍。

2)主语+谓语+ X times+ the size (amount, width, breadth, level, value, velocity, length…) of…
  这个句型表示净增加“1倍，是…的2倍”例如：
 The earth is 49 times the size of the moon.　地球是月球大小的49倍。

3)主语+谓语+ X times + 形容词（副词）比较级+ than…
  这个句型表示的数为净增加数。例如：
 The grain output is one time higher this year than that of last year.
　今年比去年粮食产量增加一倍。
 
4)还可以用by+倍数，表示增加多少倍
　The production of grain has been increased by four times this year.
　今年粮食产量增加了4倍。