The correct answer is: a) Prisoners of war.
Some tribal societies in Arunachal Pradesh practiced limited forms of slavery, often involving prisoners of war. These prisoners were often forced to work as servants or laborers for their captors. In some cases, they were also used as sacrifices or in other rituals.
Debt bondage is a form of slavery in which a person is forced to work to pay off a debt. Caste-based servitude is a form of slavery in which a person is born into a caste that is considered to be inferior and is forced to work for members of a higher caste. Kidnapping is the act of taking someone against their will.
It is important to note that slavery is a crime against humanity and is prohibited by international law.