To answer the above question, the relevant sentence is: Saint Thomas (Spanish: Santo Tomas; Dutch: Sint-Thomas; Danish: Sankt Thomas) is one of the Virgin Islands in the Caribbean Sea and, together with St. John, Water Island and St. Croix, form a county and constituent district of the United States Virgin Islands (USVI), an unincorporated territory of the United States.
This justifies what answer for what question? Q & A:
Passage: Saint Thomas (Spanish: Santo Tomas; Dutch: Sint-Thomas; Danish: Sankt Thomas) is one of the Virgin Islands in the Caribbean Sea and, together with St. John, Water Island and St. Croix, form a county and constituent district of the United States Virgin Islands (USVI), an unincorporated territory of the United States. Located on the island is the territorial capital and port of Charlotte Amalie. As of the 2010 census, the population of Saint Thomas was 51,634 about 48.5 % of the US Virgin Islands total. The district has a land area of 32 square miles (83 km).

Question: Based on this passage, where is the island of st. thomas located?
the Caribbean Sea