The correct response is:
The acting president may retain office for a maximum of 10 years as long as there are more than two years left in the previous president’s term.
According to the 22nd Amendment to the U.S. Constitution, if a vice president succeeds to the presidency and serves more than two years of the previous president's term, they can only be elected for one additional full term. If they serve less than two years of the previous term, they can be elected for two full terms. Therefore, the maximum they can stay in office is 10 years if they take over a presidency with more than two years remaining.