The judges' combined score moved the competitor to the top of the scoreboard. The correct answer is A. This is because the sentence says it is a "combined score," meaning that there are more than one judge involved in the decision-making process. Thus, the plural form of the word judge is judges, and if you want to show the possessive form of that plural word, you just have to add an apostrophe. So, judges' score means that it is a score that belongs to numerous judges. B would mean that there is only one judge, C is incorrect because you need the possessive form of the word, and D doesn't exist.
