Final answer:
The beginning of Spanish colonial rule can be traced back to the establishment of the first missions. These missions were integral to Spanish colonization efforts across the Americas, including in areas like Texas. Hence, the correct answer is option (C).
Step-by-step explanation:
Spanish colonial rule in the Americas began after Christopher Columbus's voyages of discovery in 1492, which were sponsored by the Spanish Crown. The explorations led to the claim of vast territories and establishment of Spanish colonies. However, if we are discussing the context of Texas and the options provided, the Spanish colonial rule largely began with the establishment of missions to convert the local Native American population to Christianity. The question might be referencing the broader Spanish colonization or specifically the colonization of Texas.
The answer is Option C, 'When the first missions were opened.' Missions were a common means by which the Spanish established their presence and began to exert control in new territories during the colonization of the Americas. San Antonio, for example, is well-known for its missions, including the famous Alamo, which was originally established as Mission San Antonio de Valero in 1718.