The correct option regarding how long a vice president can stay in office if they take over the presidency is:
The acting president may retain office for a maximum of 10 years as long as there are less than two years left in the previous president's term.
This is based on the 22nd Amendment to the U.S. Constitution, which states that a person can be elected to the office of President for a maximum of two terms (which is 8 years). However, if a vice president assumes the presidency due to the previous president's vacancy, they can serve the remainder of the term and still seek election for two full terms, potentially allowing them to serve up to 10 years in total if they take over with less than two years left in the original president's term.