Explanation:

- Option 1: We watched the workmen

This part of the sentence is grammatically correct and clearly states the action being observed.

- Option 2: No Error

This would indicate the entire sentence is correct, which is not true in this case.

- Option 3: of the kitchen

This prepositional phrase correctly identifies which tiles are being repaired.

- Option 4: to repair the tiles

The error lies here. Instead of "to repair," it should be "repairing" to accurately describe the ongoing action seen: "We watched the workmen repairing the tiles."

- Correct Answer: Option 4 — to repair the tiles