The correct answer is B) African Americans.
The group that included the only US soldiers that were used as reinforcement for Allied units and put under foreign command during World War 1 were African Americans.
African American soldiers represented great support to the Allied forces in Europe. The first African American troops arrived in France in 1917. The 369th United States Infantry joined the French army in the war front. For their ferocity in war and the way they defended their position, this African American army unit was known as the "Harlem Hell Fighters."