（上面蓝色字体就是系列一和二，点击就可以！）
用尽量快速和精简的方式讲授最经典的真题难句。
每个句子我会控制在两分钟以内。
你们听完以后需要用同样流畅的中文重复出来。
50句之后你的句子理解能力和翻译能力会有质的飞跃。
09年第二篇文章第六段四句话！
第一句：
Critics also argue that commercial genetic testing is only as good as the reference collections to which a sample is compared.
第二句：
Databases used by some companies don't rely on data collected systematically but rather lump together information from different research projects.
第三句：
This means that a DNA database may differ depending on the company that processes the results.
第四句：
In addition, the computer programs a company uses to estimate relationships may be patented and not subject to peer review or outside evaluation.
