Final answer:
The Dominican Republic is not a U.S. territory, whereas American Samoa, Puerto Rico, and Guam are U.S. territories, which have non-voting delegates in Congress except for residents of D.C.
Therefore, option C is correct.
Step-by-step explanation:
The correct answer to the question "All of the following are United States territories EXCEPT:" is C. Dominican Republic. The Dominican Republic is a sovereign state located in the Caribbean and is not a U.S. territory. The United States territories include American Samoa, Puerto Rico, and Guam, among others. These territories do not have full representation in Congress and have a non-voting delegate, except for the residents of the District of Columbia who also lack voting representation in Congress.