d. They used the image of a horse beneath a political figure to help convey the subject supreme power and leadership.
Explanation:
The reason behind the answer is because first, the first examples of equestrian portraits are not from the 19th century. People have been portraying themselves on horses since the Chinese dynasties before the unification of china. Second, exaggerating facial features is not a rule for equestrian portraits. Third, it didn't become popular just because Picasso used it to manifest his discontent. People have loved horses since they domesticated them. Fourth, they always used horses to provide political figures another level of superiority, Napoleon white horse portrait is an example, his horse was a monster, while he was pretty short.
