Explanation:

- Assimilation: This refers to the process where individuals or groups from one culture adopt the traits of another culture, eventually losing their original identity.

- Acculturation: This is when one society learns or adopts elements from another culture, but both cultures retain distinct identities.

- Diffusion: This is the spread of cultural traits from one society to another, but not necessarily by learning or direct adoption—more about ideas or innovations moving across cultures.

- Cultural expansion: This is a broader term, usually referring to a culture’s influence spreading in general, not specifically by learning or borrowing.

Correct Answer: Option 2 - Acculturation