Prior to 1497, how were goods transported from india and china to europe?

What would lead a historian to consider two events to have a relationship of correlation rather than causation

What was one cause of the decembrist revolt? a. the desire for a constitutional monarchy b. the need for workers’ reforms c. the creation of a new railway line d. the outcome of the crimean war

During the era of european expansion, what was the biggest reason for spain’s push for exploration?