The correct answer is d. to visit holy places. The pilgrims traveled in order to visit holy places that held religious significance for them. To arrive at this answer, you could start by eliminating the other options and focusing on the term "pilgrims." Pilgrims are typically people who undertake a journey, often for religious purposes. So, options a (to fight a holy war), b (to organize followers), and c (to pay tribute to a king) do not align with the definition of pilgrims. By process of elimination, you can conclude that the pilgrims traveled to visit holy places.