Explanation:

- Cover up typically means to hide or conceal something, often referring to hiding the truth or details of an event or action.

- Option 1: Put a carpet under isn't widely recognized as an idiom and doesn't relate to "cover up."

- Option 2: Ignore insults made suggests turning a blind eye to verbal attacks, which doesn't align with the meaning of "cover up."

- Option 3: Hide or conceal directly correlates with the action of concealing something purposefully, matching the idiom "cover up."

- Option 4: Close something forever indicates finality, but it doesn't fit the context of obscuring or hiding details.

Option 3: Hide or conceal is the correct answer for the idiom "cover up."