Answer: year's.
Explanation: The possessive form is used with nouns (Names of people, places, animals or objects) to show a relationship of belonging between two or more things. The possessive form is formed adding an apostrophe and the letter "s" to the noun. If the noun is plural or it ends in "s" we just add the apostrophe after the "s." In this case, the noun we need to transform in its possessive form is "year" so we add an apostrophe and "s" and it becomes "year's."
