Which sentences use the possessive form correctly?

The sentence that uses the possessive form correctly is the one that mentions "my sister-in-law's house." This construction effectively indicates that the house belongs to your sister-in-law, demonstrating the appropriate use of the possessive form by adding an apostrophe and 's' to the noun "sister-in-law." This construction is clear and grammatically accurate.

In contrast, the other sentences do not correctly apply possessive forms. The second option involves the word "Politics'" which is less commonly used in possessive constructions, as "politics" is generally treated as a singular noun that doesn't usually take a possessive form. The third option doesn't contain any possessive forms, simply stating a proverb without any indication of ownership. The fourth option employs "the box's label," which is technically correct, but this is less common and can sound awkward compared to other ways of expressing ownership in everyday language.

Ultimately, the first option stands out due to its clarity and conventional usage in the possessive form, making it the most appropriate choice.