To find the median score for this year, we need to order the scores from lowest to highest. The scores are 233, 456778, 7889, and 999. The median is the middle score, which is 7889. To find the median score for last year, we need to order the scores from lowest to highest. The scores are 6654, 97753, and 995. The median is the middle score, which is 97753. The difference between the median score this year and the median score last year is 97753 - 7889 = 89864. Therefore, the answer is A. 89864.