There are two classes, two broad classes of drug sort of type ligands that are defined, agonists and antagonists.

这样的配体药物有两类,目前已经明确的配体药物大体上分为两种,分别是激动剂和拮抗剂

耶鲁公开课 - 生物医学工程探索课程节选

On one level, there are things like companies that have two . different classes of stock that are economically identical.

一方面，我们有这样的例子，有的公司拥有两种,不同类别的股票，他们在经济意义上是相同的。

耶鲁公开课 - 金融市场课程节选

There are two general classes of molecules that are produced by the endocrine system.

内分泌系统产生的分子通常有两类

耶鲁公开课 - 生物医学工程探索课程节选

There are basically two classes of testing.

基本上来说测试分为两种。

麻省理工公开课 - 计算机科学及编程导论课程节选