The correct answer is "Gruesome twosome, Grusome twosome, grewsome twosum." This hink pink is a wordplay riddle where the answer consists of two rhyming words that hint at the given clue. In this case, the clue "A gross pair" suggests a pair of things that are unpleasant or repulsive, which can be described as "gruesome." The rhyming word "twosome" indicates that there are two of these unpleasant things. Therefore, "Gruesome twosome" is the correct answer, and the variations "Grusome twosome" and "grewsome twosum" are also acceptable due to the similarity in pronunciation.