Explanation:

- Option 1: Zero-sum mobility

- This refers to a situation where upward movement by some people only happens if others move down. The total "amount" of status is fixed.

- Option 2: Horizontal mobility

- This means changing jobs or roles that have similar social standing, so there is no movement up or down in the social hierarchy.

- Option 3: Inter-generational mobility

- This is when children experience a different social standing than their parents, i.e., social movement across generations.

- Option 4: Intra-generational mobility

- This is about upward or downward movement in a stratification system within the span of a single person's career; social status changes within one's own lifetime.

Correct Answer: Option 4: Intra-generational mobility