Explanation:

- Option 1: R.A. Nisbet

- He was known for work on social traditions and conservatism, but he did not explicitly divide societies into "folk" and "urban" types.

- Option 2: L.H. Morgan

- He classified societies as "savagery," "barbarism," and "civilization," focusing on evolutionary stages, not specifically "folk" and "urban."

- Option 3: G. Lenski

- He analyzed societies based on technology and types like "hunter-gatherer," "agrarian," etc., not "folk" and "urban."

- Option 4: Robert Redfield

- He is known for distinguishing societies as "folk" (small, tradition-bound) and "urban" (larger, more complex), especially in his work "The Folk Culture of Yucatan."

Correct Answer:

Option 4: Robert Redfield