Translation of "Classified" in Chinese

The classified documents were hidden.

机密文件被藏起来了。

In the post office, mail is classified according to the place where it is to go.

邮局根据寄信地址将邮件进行分类。

Data compression algorithms can be classified in two categories: those with data loss and those without data loss.

压缩数据的算法能分为两种：一种会造成数据损失，另一种则不会。