Explanation:

- Class, gender, and caste are all forms of social stratification. This means that society is divided into hierarchical layers based on factors like wealth (class), identity (gender), or birth (caste).

- Sex is a form of differentiation. It simply refers to biological differences between males and females and doesn't by itself establish a hierarchy.

- Social stratification involves ranking groups; differentiation just distinguishes between them without ranking.

- So, the correct answer is:

- Option:4, Sex