Answer
The first guideline is level C, the second guideline is level A, and the third guideline is level B.
Work Step by Step
The second guideline is clearly the strongest evidence, as it comes from rigorous testing with good experimental setup and thus gives results that are very likely true. The first guideline is the weakest evidence, as the poor experimental setup invalidates any conclusions from those studies. The third guideline is in the middle, since expert opinion could be fallible compared to rigorous clinical trials, but experience is probably better than poor statistics.
