The interactions described in the letters are best understood in the context of which of the following?

(A) Portuguese exploration of the coast of West Africa (B) Catholic missionary efforts in Sub-Saharan Africa (C) State formation in Sub-Saharan Africa (D) Development of the slave trade in Sub-Saharan AfricaExplanation: Both sources mention slavery either as the main point (Source 1) or in passing as a commodity (Source 2). Eliminate answer choices that do not focus on slavery. Choices (A), (B), and (C) do not mention slavery, so (D) is the answer.