Which of these vehicles is likely to be used for medical evacuation?

The M113 is the correct choice for a vehicle likely to be used for medical evacuation because it is designed as an armored personnel carrier that can be adapted to various roles, including medical evacuation. Its spacious interior allows it to carry injured personnel comfortably while providing some level of protection from enemy fire. The M113 can be equipped with medical equipment and stretchers, making it ideal for transporting casualties in a combat environment.

In contrast, the other vehicles listed serve different primary functions. The M969 is a fuel tanker designed for logistics, the M978 is a fuel and water servicing vehicle, and the M984 is a heavy wrecking truck primarily used for recovery operations. While these vehicles have important roles in an operational setting, they are not designed for the specific purpose of medical evacuation.