The correct answer is A, the individuals described in the headline would have most benefited from Truman's Executive Order 9981, as it was a military-related decree that prohibited discrimination within the U.S. Armed Forces.
Here is a short review of each option:
A- Truman's Executive Order 9981: Executive Order No. 9981 is a Presidential Decree of US President Harry S. Truman dated July 26, 1948, granting equal treatment and equal opportunities to all members of the United States Armed Forces, regardless of race, color, religion, or national origin.
The decree was welcomed by the African American community as the end of racial segregation in the armed forces and is still considered an important step towards abolishing racial discrimination.
B- The War Powers Act: The War Powers Act is a US Federal Law passed in 1973. It provides that the president must obtain congressional authorization to hire troops abroad for more than 60 days.
C- The National Labor Relations Act: The National Labor Relations Act (also known as the "National Labor Relations Act") also called the Wagner Act ("Wagner Act" by Senator Robert F. Wagner, who promoted it) is a federal law of the United States issued in July 1935 to limit the reactions of employers against workers who found unions, collectively offer their services, join strikes, or perform similar acts of defense of their rights in concert, whether forming a union or without it. This Law was not applicable to workers subject to special regimes: railway workers, agricultural workers, domestic workers, independent contractors, or workers of the federal or state government, having these their own norms.
D- Roosevelt's Executive Order 8802: Executive Order 8802 was signed by President Franklin D. Roosevelt on June 25, 1941 to prohibit racial discrimination in the defense industry of his country. It was the first federal action to promote equal opportunities and to prohibit discrimination in employment in the United States.