VOA慢速英语:Americans love Christmas trees

短语讲解：

1. The National Christmas Tree Association says more than 35 million of them were bought last year in the United States.

more than 不只是; 很; 超过; 在…次以上
例句：More than 1000 turned up.
最后共有1000多人出席。

2. It estimated that 10.9 million artificial trees were sold in 2012, compared to 24.5 million natural trees.

compare to 把…比作， 喻为; 与…相比
例句：They have nothing to compare to.
没有东西让他们来比较。

3. To make sure there is always a supply, farmers usually plant one to three new saplings for every tree they cut down.

make sure 把事情弄清楚，核实或查明某事物
例句：How do you make sure this is clear?
你怎么能确定这足够明确呢？
cut down 裁短; 减少
例句：That should cut down on roadworks, and therefore on jams.
这肯定削减了道路施工量，所以道路仍然拥堵。

4. They were placed near large hills of sand to prevent the sand from blowing away.

prevent from 阻止， 防止
例句：Active cure of swoon patients was important to prevent from complications.
积极救治晕厥患者，对预防并发症有重要意义。