No D, is not the most common answer. Or at least DO NOT TRY TO GUESS D.
Despite statistics, the creators of AMC 8 are AWARE of this fact, and they take advantage of this.
The answers are prettry random, and D happens to be the most common answer.
If you want to do good, I HIGHLY recommend to practice the first FIFTEEN minutes untimed. Try to think about it, take as long as you want. Then time your self once you are good.
If you get to a point where you score an average of 20 or above on the old AMC 8s, and a 15 or above on the recent ones, you should be set!
However, that is insanely hard, and I rarely get to that point. The best I gotten was a 23, but my average is like a 14.
The most common mistake is SILLY errors, so try double checking your first 15 problems. Then just attempt the last ten.