Final answer:
Document C, written by Velleius who was a soldier during Augustus' time, highlights the accomplishments and reforms of Augustus and was written during his reign.
Step-by-step explanation:
Document C was written during the reign of Augustus. Velleius, who wrote the document, provides a firsthand account of his experiences while serving as a soldier under the rule of Augustus. Therefore, the correct choice would be a) During the reign of Augustus. The passage describes the numerous contributions Augustus made to Rome, including ending civil wars, restoring peace, reforming laws, and refusing dictatorship, which indicates it was composed during his period of influence. The reforms and titles Augustus adopted led to the establishment of the Roman Empire, with his consolidation of power and restructuring seen as crucial to Rome's transformation and subsequent stabilization.