The correct option is
A Yours
Pronouns are the words that replace nouns. In order to fill in the blank, we must understand what possessive pronouns are. When a person possesses/owns a thing, we can use a possessive pronoun. For example, This book is mine. Here, 'mine' is used at the end of the sentence to show possession, instead of the word 'my'.Option B - 'Your' is a personal pronoun. As the given sentence talks about the possession of the book, we need a pronoun in the possessive case. Hence, option B is incorrect.
Option C - 'Our' is a personal pronoun and can't be used in the possessive case here. Also, the sentence is about the second person pronoun. 'Our' is a first-person pronoun. Hence, option C is incorrect.
Option D - 'Ours' is a possessive pronoun, but it is a first-person pronoun. Hence, we can't use 'ours' here. Thus option D is incorrect.
Option A - As the given sentence needs a second person possessive pronoun, we can use 'yours' here. 'Yours' is used to show the second person's possession/('s). As the sentence demonstrates the book that the first person (my) and the second person possessive pronoun (yours) possess, 'yours' is correct. Hence, option A is the correct answer.
'This is my book and that is yours.'