Explanation:

- The Assam Sahitya Sabha, a literary organization established in 1917, has made a statement regarding language requirements for working in Assam.

- The decree specifies that people who do not know Assamese or any other indigenous language would not be allowed to work in the state.

- The organization has also urged the government to introduce indigenous languages as the third language in schools up to Class 12 within a month.

Options Analysis:

- Option 1: but - "but" is a conjunction used to contrast ideas, which doesn't fit the context.

- Option 2: nor - "nor" is used in negative sentences and usually follows "neither," which doesn't fit here.

- Option 3: or - "or" is used to present alternatives or options, which fits perfectly in the context.

- Option 4: so - "so" indicates a consequence, not suitable for this sentence structure.

Correct Answer: Option 3 - or