Amendment 6 guarantees a speedy trial which is public and assessed by a jury that is chosen as easily as it can be accomplished to be impartial. It also makes a requirement that the defendant must understand the charge. And he has the right to question his accusers and present witnesses who will speak on his behalf.
D really doesn't matter. Americans are governed by their own constitution, not the constitution and laws of other nations.
Not A: Though 12 is not a magic number (6 jurors could be chosen and that number will be enough), the supreme court has ruled that the number of jurors cannot go below 6. I don't think there is an upper limit, but common practice is 12 and almost any crime can be tried by a jury if the amount involved is over 20 dollars. (That's amendment 7). I don't think A is what you want.
The other 2 are covered by D. I honestly don't think there is a good answer to this question. Sometimes you get questions like this. I suppose that since you cannot pick anything else, pick D, but a warning. It could be A or B. The right to a speed open trial where the charge is understood, is what the constitution guarantees.
