We feel that the best answer is “b”, as both events involved the deaths of large number of Native Americans, including non-combatants:

1. The Trail of Tears: “The Trail of Tears was the relocation and movement of Native Americans, including many members of the Cherokee, Creek, Seminole, and Choctaw nations among others in the United States, from their homelands to Indian Territory (present day Oklahoma) in the Western United States. The phrase originated from a description of the removal of the Choctaw Nation in 1831. Many Native Americans suffered from exposure, disease, and starvation while en route to their destinations, and many died, including 4,000 of the 15,000 relocated Cherokee.” (Wikipedia)

2. Battle of Wounded Knee: “On December 29, 1890, 365 troops of the U.S. 7th Cavalry Regiment, supported by four Hotchkiss guns, surrounded an encampment of Miniconjou (Lakota) and Hunkpapa Sioux (Lakota) near Wounded Knee Creek, South Dakota. The Sioux had been cornered and agreed to turn themselves in at the Pine Ridge Agency in South Dakota. They were the very last of the Sioux to do so. They were met by the 7th Cavalry, who intended to disarm them and ensure their compliance. During the process of disarming the Sioux, a deaf tribesman named Black Coyote could not hear the order to give up his rifle and was reluctant to do so. A scuffle over Black Coyote's rifle escalated into an all-out battle, with those few Sioux warriors who still had weapons shooting at the 7th Cavalry, and the 7th Cavalry opening fire indiscriminately from all sides, killing men, women, and children, as well as some of their own fellow troopers. The 7th Cavalry quickly suppressed the Sioux fire, and the surviving Sioux fled, but U.S. cavalrymen pursued and killed many who were unarmed. By the time it was over, about 146 men, women, and children of the Lakota Sioux had been killed. Twenty-five troopers also died, some believed to have been the victims of friendly fire as the shooting took place at point blank range in chaotic conditions. Around 150 Lakota are believed to have fled the chaos.” (Wikipedia)