Concept:Compound nouns like "father-in-law" form the singular possessive by adding an apostrophe and "s" to the whole compound noun.Explanation:The sentence refers to the house belonging to one father-in-law. Hence, we need the singular possessive form. For a singular compound noun ending in "law", place the apostrophe after the entire word, giving "father-in-law's". The form "father's-in-law" incorrectly places the possessive on the first part. Similarly, "father-in-laws" incorrectly pluralizes the compound instead of showing possession. Also, "fathers-in-law" is the plural form of the compound noun, not a possessive form. Since the sentence requires possession by a single father-in-law, the correct form is "father-in-law's".Answer:A. father-in-law's