This explanation is what got this to click. Thank you.

Thank you. You did a better job explaining this than the entire 15 minute video (11 minutes if you are only trying to figure out why A is wrong).

#feedback and also asking for help. For whatever reason, I understood what E was trying to say right away, which is really really rare for me. So I was stuck between D and E, ultimately choosing E. This explanation does a great job of translating E but never told me why D was a better choice than E. I had to actually read the "Lets Review" section to find the answer I was looking for - which was that if E was true, the 24-year study would have had the same results as the 12-year study and thus no discrepancy at all. (so I guess in the end I didn't understand E as well as I thought I had)