Question: Trade beads (sometimes called aggry and slave beads) were otherwise decorative glass beads used between the 16th and 20th century as a token money to exchange for goods, services and slaves (hence the name), this included the African slave trade, slavery has existed in Africa for how long?
{'answer': 'many centuries', 'supporting_facts': [['Trade beads', 2], ['Slavery in Africa', 0]]}