In the exam can solve the answers at parts... example..first solve ques no 1(a) then 2(b),5(a),1(d)so on...means can solve the paper in any sequence...
you can solve but it will be good if you don't follow this type of practice solve all part of single question say 2 (b), (c), (a) & then go for any other 1 or 3 or any other
you Can, but see to it that you complete the whole question in one order, and not write answer 2a, then 3d, then come back to write 2b and 2c... if you want to write in your own order, you Can it's up to you.