D1's content is pretty simple to understand and implement, but tough to do well in exams. You have to handle a big set of data and narrow it down with perfect accuracy, as very few method marks are given over the course of six questions. This does also mean that provided you make no silly mistakes, it's relatively easy to get high marks.
When you drop marks in exams, is it more commonly method marks or accuracy marks? If it's the first one, you will ace D1, no problem.