To answer this question, one has to be familiar with boundary value analysis. For those who are not familiar with this (as I was not when I first came upon this question), it is simply a testing software used to find errors at the input and output edges of a set range, instead of those in the middle. So, to test these, there are usually six numbers involved: the minimum number, the minimum minus one, the minimum plus one, the maximum, the maximum plus one, and the maximum minus one.
Therefore, it is easy to conclude that answer B (4, 5, and 99) is correct. However, according to this explanation of boundary value analysis, answer C (5, 100, and 101) would also be correct.