Final answer:
Navy admirals can approve the Legion of Merit for all Navy personnel and for members of other U.S. Armed Forces who are grade O-6 and below in their chain of command.
Step-by-step explanation:
The Legion of Merit is a military award that can be granted by various ranks within the U.S. Armed Forces, including admirals in the Navy. According to regulations, admirals who hold the rank of O-10 may approve the Legion of Merit for all Navy personnel under their command.
When it comes to other U.S. Armed Forces personnel such as those from the Marine Corps, Army, Air Force, and Coast Guard, an admiral can approve the award for members of these branches who are O-6 and below in their chain of command. Therefore, the correct answer to the question is c) O-6.