直到最近在分类学上，鸟的定义是一只有羽毛的动物。

Taxonomically, the very definition of a bird was until recently an animal that has feathers.

youdao

我们已经开发出了一套给动物物种分类的原则。

We have developed a system to classify animal species.

youdao

我们已经开发出了一套给动物物种分类的原则。

We have developed a system to classify animal species.

youdao