Step 1: Identifying the correct option:
Social stratification refers to the socially constructed, hierarchical ranking of people based on factors like caste, class, wealth or status. Height is a natural, physical/biological attribute, not a socially constructed basis of ranking - so it is not a form of social stratification.
Step 2: Why the other options are wrong:
Caste, class and the (historical) estate system are all classic, well-recognised systems by which societies rank and divide people into hierarchical layers.
Final Answer:
Height (Option B)