the keys to the success of the mongolian military in the 1200s included\na fleet of powerful ships.\na…

Brief Explanations:

To determine the key to the Mongolian military's success in the 1200s, we analyze each option:

• "A fleet of powerful ships" is incorrect because the Mongols were known for their land - based and horse - based warfare, not naval power.
• "A single squad of soldiers" is wrong as the Mongolian military had a large and organized force, not a single small squad.
• "Organized troops on horseback" is correct. The Mongols were famous for their highly organized cavalry units, which were very mobile and effective in battle.
• "Rifles and other advanced weapons" is incorrect because rifles were not developed during the 1200s.

Answer:

C. organized troops on horseback.