Answer: The rider tugged on the reins of her horse to make him slow down.
Explanation: 'Reins', which is a noun, is a word used to refer to a long strip of flexible material that is attached to a horse in order to control it and make it stop when it is necessary. In that way, "reins" is the word that fills in the blank since the rider is trying to direct her horse. In contrast, the words "ranes", "rains" and "reigns" are not related to the context of the sentence; therefore, they could not fill in the blank.
