For a rational number to generate a repeating decimal, the denominator must not evenly divide any power of 10.
In other words, if the rational number is in the form \(\frac{a}{b}\) (where \(a\) is the numerator and \(b\) is the denominator), the decimal will be repeating if \(b\) contains any prime factors other than 2 or 5. If \(b\) is only made up of the primes 2 and 5, the decimal will terminate.
So, the correct answer is: The denominator must not evenly divide any power of 10.