Explanation:

- Option 1: Ethnic group

- This refers to people sharing common cultural, racial, or national traits.

- A press group is not generally organized by ethnicity.

- Option 2: Informal group

- These are loosely formed groups, like friends or workmates.

- A press group is more formal and organized with a purpose.

- Option 3: Special interest group

- These are organized groups aiming to influence public policy or promote specific issues.

- A press group seeks to protect and promote the interests of media and journalists, making it a special interest group.

- Option 4: Caste group

- Refers to people of the same caste, mainly in South Asian context.

- Has nothing to do with press groups.

Correct answer: Option 3: Special interest group