科学家们正在根据动物的栖息地进行分类。

Scientists are working on the ___classifications of animals based on their habitats.

这些产品根据质量分为三个等级。

These products are divided into three ___classifications based on quality.

生物学家正在讨论这些昆虫的分类问题。

Biologists are discussing the ___classifications of these insects.