Answer: The sentence that reflects the correct usage of a plural possessive noun is "Olympic snowboarders' determination drives them through the rigorous training required to remain competitive in the sport".
Explanation: A possessive noun is formed by adding an apostrophe and an "s" at the end of a noun. However, if the noun is plural, only an apostrophe is added at the end of the noun. As "snowboarders" is a plural noun, the only element that should be added at the end of the word is the apostrophe ('). Therefore, the only sentence that reflects the correct usage of a plural possessive noun is "Olympic snowboarders' determination drives them through the rigorous training required to remain competitive in the sport".