In the sentence 'The capital of the United States is in Washington,' the word 'Washington' (a place) refers to:

On the USCIS reading vocabulary list, WASHINGTON appears both as a PERSON (George Washington) and as a PLACE (Washington, D.C.). In a sentence about the 'capital of the United States,' Washington refers to the place — Washington, D.C., where the federal government is located. The reading test expects applicants to recognize PLACES vocabulary such as Washington (D.C.) and the United States in context. Distinguishing the place from the person based on the sentence's meaning is exactly the kind of comprehension this section measures.