A number that is rational is a number that can be written as a decimal, a/b, with b not equal to 0. We can start by eliminating some options. Pi is not rational (it keeps on going). In addition, B is not rational because it doesn't seem to have an end. In addition, A is not rational to because that number can't be expressed as a fraction. But, C can. C can be expressed as the fraction 1/3 (that is infinite threes going on forever). Since it can be expressed as a fraction, C is the answer.