What are those?They are __ my sister's textbooks my sister her textbooks my sister textbooks the textbooks my sister

The correct answer is "her textbooks." Here's the explanation:In this sentence, "What are those?" we need to determine the possessive pronoun that correctly refers to "textbooks" belonging to "my sister."- "my sister's textbooks" is grammatically correct but not one of the options.- "her textbooks" is the correct possessive pronoun form.- The other options do not form grammatically correct sentences.So, the complete sentence would be: "What are those? They are her textbooks."