One key reason is that people use their cell phones, by definition, in ways that make them hard to study.

按定义，一个关键的理由是，人们使用手机的方式使得研究比较困难。

youdao

One key reason is that people use their cell phones, by definition, in ways that make them hard to study.

按定义，一个关键的理由是，人们使用手机的方式使得研究比较困难。

youdao