When thinking about this problem, you have to understand what happens when you multiply something by a fraction less than 1.
If you multiply a number by 1/2, the result is going to be less than the original number. Same thing happens when you multiply it by 3/4, or 5/6, or even 99/100 - as long as the fraction is less than 1, the original number gets smaller when you multiply it by that fraction.
If you multiply a number by a number greater than 1, however, the result ends up being greater than the original number. For example, multiplying 5 * 2 gives you 10, which is greater than 5.
The second thing to remember is that an exponent is just a fancier way of multiplying a number by itself. For example, all that "1/2 to the 3rd power" means is multiplying 1/2 by itself 3 times, or 1/2 * 1/2 * 1/2.
So, combining these thoughts, we reach the fact that the answer must be 5 to the fifth power.
All of the other answer choices give fractions less than 1. When you take those fractions and give them an exponent, all you're doing is multiplying them by themselves, and multiplying any number by a fraction less than 1 makes the result smaller than the original. 5 is the only number involved that is greater than 1.