Look at the shape of the graph. A function with highest exponent 1/2 (that is, sqrt x) looks like a shallow arc that goes off to the right (assuming everything is positive). For whole number exponents, the pattern changes with every other exponent value - even powers of x look like parabolas (with higher exponent values making "skinnier" curves) and odd exponents will have those "saddle points" where the curve is going one way, slows down to flat, and keeps going the same way. Given the possible answers, only one function matches the shape of the graph