The Denarius of Julius Caesar was the currency (coin) that was introduced in 44 B.C. It was the first time that the portrait of a living person was used on coins. The Denarius had the portrait of Caesar in front (the observe) and the picture of Venus at the back (the reverse) - this was to ascert Caesar's divine ancestry. The Denarius of Julius Caesar was a widespread way of projecting the power, achievements and consequently, the propaganda of the Roman empire to both the literate and non-literate populace (everyone knows the name "Caesar").
Augustus of Primaporta is a work of art; it is a full length statue of Augustus Caesar (the first Emperor of Rome) towering at 2.08 m and weighing 1000 kg. It employed the use of many distinctive art features to project the power and propaganda of the Roman empire.
Emperor Justinian and His Attendants is a Byzantine styled colorful and detailed apse Mosaic painted in 547 A.D. The Mosaic depicted the Emperor Justinian standing at the center in front of both clergy and military men. The message the Mosaic protrudes is that the Emperor is the one ordained to rule and that he has the power to. It projects the power and authority of the Emperor Justinian.
Hence, the common feature of these trio is option C - propaganda (spreading of information to help a cause or institution).
