Final answer:
The source for slaves transported to Madagascar was East Africa, where the Swahili coast played a significant role in the trade, influenced by European slave trading activities.
Step-by-step explanation:
The source for slaves who were transported to Madagascar was D. East Africa. The Swahili coast was a key region involved in this slave trade, where merchants purchased enslaved Bantu peoples from the interior through African intermediaries, and ships transported them to various places including Madagascar. The activities of European slave traders in the seventeenth and eighteenth centuries intensified the scope of the trade, and indeed, people from East Africa were sold into slavery not just in the Indian Ocean network but also in the Americas.