Final answer:
Guam is the island of Oceania under U.S. administration, making the correct answer C. Guam. It is a key strategic territory of the United States, along with other islands like the Northern Mariana Islands and Wake Island.
Step-by-step explanation:
Among the islands of Oceania, Guam is considered to be under U.S. administration. Therefore, the correct answer to the given question is C. Guam. Guam is an important strategic location for the United States and is an unincorporated territory. Other U.S. territories in Oceania include the Northern Mariana Islands and Wake Island. The Northern Mariana Islands are situated close to Guam and, along with Wake Island, are under U.S. sovereignty. The Federated States of Micronesia, which once formed part of the United Nations Trust Territory administered by the United States, now have an independent status but are in a Compact of Free Association with the United States.