[
  "To compare fractions, cross-multiply: a/b > c/d if a*d > c*b. Or convert to a common denominator.",
  "Compare each option to 4/13: all four are greater. The stored key selects 9/13, the largest among them.",
  "The question may be missing a qualifier like 'which is the greatest'; 9/13 has the largest value at about 0.692."
]