Concept:An improper fraction has a numerator greater than or equal to its denominator.Explanation:Check each option:Option A: 51​ and 52​ — both numerators are less than denominators. They are proper fractions.Option B: 31​ and 51​ — again, numerators are smaller. Proper fractions.Option C: 57​ (7 > 5) and 34​ (4 > 3). Both are improper fractions.Option D: 4 is a whole number, and 81​ is a proper fraction. Not both improper.Thus, only option C contains two improper fractions.Answer:C. 57​,34​