Assertion (A): During the time of Akbar, for every ten cavalrymen, the mansabdars had to maintain twenty horses. Reason (R): Horses had to be rested while on march and replacements were necessary in times of war.

The correct answer is A because both the statement and the reason are historically accurate and logically linked. Under the Mansabdari system established by Akbar, the Dah-Bisti rule or ten-twenty rule was implemented. This rule required a mansabdar to maintain two horses for every single cavalryman. The primary reason for this requirement was practical necessity. During long marches and military expeditions, horses would often get exhausted, injured, or die in battle. Having a ratio of two horses per soldier ensured that a fresh replacement was always available, keeping the cavalry mobile and effective during warfare. Since the reason provided directly explains why the specific ratio mentioned in the assertion was maintained, A is the correct option.