In which medium are the depictions of Justinian and Theodora in San Vitale made?

a. panel painting
b. low relief sculpture
c. fresco
d. mosaic
e. freestanding sculpture

d. mosaic

a. Incorrect. Panel painting was not an important medium for royal depictions at the time.
b. Incorrect. Though low-relief sculptures exist at the time, these depictions are not sculpted.
c. Incorrect. These royal portraits are not frescos.
d. Correct. These highly sophisticated and rich mosaics are appropriate for such royal portraits.
e. Incorrect. These portraits are not freestanding sculpture.