Cave and rock paintings indicate which horse breed was ridden by the Vikings?

Cave and rock paintings provide valuable insights into historical human activities, including the domestication and usage of horses. The Vikings are known to have used the Fjord horse, which is a breed originating from Norway. The distinctive characteristics of the Fjord, including its strong build and adaptability to harsh environments, made it an ideal mount for the Vikings during their explorations and conquests.

Evidence from historical contexts, such as artifacts and artistic representations, supports the association between the Fjord horse and Viking activity. This breed's agility and endurance were particularly useful for the Viking lifestyle, which often involved long voyages and varied landscapes.

In contrast, the other breeds listed were either not present in the Viking era or do not have associations with Viking culture. For example, Appaloosas are primarily associated with Native American cultures, Clydesdales have Scottish origins and were used more for heavy draft work, and Mustangs are closely linked to the American West and not to Viking history. Thus, the Fjord horse stands out as the correct answer due to its historical relevance and practical qualities that suited the lifestyle of the Vikings.