take them all IMO.
But I understand that may not be too feasible:
Here is my own rundown of the forms
1,3,4- Not too difficult
2- Most difficult form (though only by nature of the wording/structure of the question and a heavier emphasis on the molecular biology/ genetics)
5- Easiest form.
6/7- I felt my brain churning the whole time to process information
11- Not particularly hard
12- A few tricks in there, but one can work things out.
Bottom line:
If there were only two you could do, go for 6 and 7.