Correct Answer: (c) you sit on it and control its
Solution:"It's" is a contraction and should be used where a sentence normally reads "it is", the apostrophe('s) indicates that part of a word has been removed like It's raining is a contraction of It is raining. Whereas, "Its" with no apostrophe('s) is the possessive form of the pronoun 'it' which means belonging to it like the dog hurt its tail. Similarly in the given sentence, 'movements' belong to the Horse. Hence, 'you sit on it and control its movements' is the most appropriate answer.