Answer: Choice C only
The number pi = 3.14159... is irrational because it cannot be expressed as a fraction of two whole numbers. The same can be said about the square root of 99 and the square root of 21. Note how sqrt(99) = 9.9499 approximately and sqrt(21) = 4.5826 approximately; neither of those results are whole numbers. In contrast, sqrt(225) = 15 which is a whole number so sqrt(225) is rational. It can be expressed as 15/1. So everything in choice C is either a fraction or it can be expressed as a fraction. Note: mixed numbers can be converted to improper fractions.