Difference Between Answers C & E

@Adamd, Let's look at (C) and (E). With (C), it's very close, but you're right—the phrase "more important" is what makes it wrong. The statistics show that there are other factors, but we have no idea whether or not any of these additional factors are more important, so (C) is too strong with its wording and can be eliminated. (E) says precisely what we're looking for. The statistics show that the number of police isn't the only factor and that there must be other factors that are influencing the rates of crime, so this is why (E) is correct. Hope this helps. Let us know if you have any other questions!

Got it, thank you very much!

@Adamd, you're welcome!

I also feel that the word "prove" is much too strong to support the use of statistics in this question. We'd need something weaker, such as "suggest"