Which of the following is a rank in the Navy?

The answer is valid because "Chief Warrant Officer Four (CWO4)" is indeed a rank within the United States Navy. The Navy utilizes a rank structure that includes both enlisted personnel and commissioned officers, and the Chief Warrant Officer ranks fall under the officer category. CWO4 is a specific designation that indicates a senior level of proficiency and responsibility within the Chief Warrant Officer ranks.

In contrast, other ranks listed have affiliations with different branches of the military. For example, "Captain" can refer to a rank in both the Navy and the Army, but its implications and responsibilities differ by service. "Sergeant" is a rank primarily associated with the Army and Marine Corps, while "Major" is a rank used in the Army, Air Force, and Marine Corps, and does not exist in the Navy's rank structure. Therefore, the identification of CWO4 as a Navy rank accurately reflects the hierarchy and classification used within the Navy.