Which statements correctly describe the african slave trade of the 1500s?

choose all answers that are correct.

a.
african slaves were needed in the americas to replace the rapidly declining population of native people.
b.
the middle passage refers to the forced journey of kidnapped africans from eastern african to western africa where slave ships waited.
c.
when african slavers sold kidnapped africans to european slave traders in the 1500s, it was the first time members of one tribe had sold members of another tribe into slavery.
d.
the transatlantic slave trade involved millions of africans kidnapped into slavery over the course of 300 years.