The correct answer is B) Muslim merchants.
From the seventh to the fourteenth centuries CE, the group that was the PRIMARY trade link between India, China, Europe, and Africa were Muslim merchants.
Indeed, there were two ways in that Islam spread to many other territories. First, through Arabian conquest, and then, by trade. Islam first spread all across the Arabian Peninsula anthem to many regions such as the North of Africa, Asia, the Middle East and faraway parts of Europe such as the Iberian Peninsula. So yes, the group that was the PRIMARY trade link between India, China, Europe, and Africa were Muslim merchants.