First you check [subject] and [verb] relation and find they are ok. Careful with the appositive phrase so it doesn't confuse you. You should notice this sentence is a comparison which means you need to compare to elements in the same way. Element 1 is population (in this state). You then go to element 2 and realize it is not following the same pattern, meaning option D marks the incorrect fragment. The prison population in this state, now at an all time high, is higher than in any state.