For a rational number to generate a repeating decimal, the denominator must not evenly divide any power of 10. This means that the denominator can have prime factors other than 2 and 5 for the decimal representation to be repeating. If the denominator is comprised solely of the prime factors 2 and/or 5, the decimal will terminate instead.
So, the correct response is: The denominator must not evenly divide any power of 10.