i take combined. 
what do you mean by all this pure and combined that makes it so
freaking complicating. ( this is what sec 2 will think) haha
!
Combined
sciences:
- you will take either physics and chem or physics or bio.
- Total mark adds together for this 2 subjects is counted as 1
subjected marks.
eg. results for test/exams:
Physics 50/100
Chemistry 50/100
report book will appear like : Sciences : 50/100
- Quite similar to pure sciences but u learn lesser things
- Easier if you understand.
- Assure an A1 or A's if u score well.
Pure
sciences:
- You will take either physics and chem and bio or physics and chem
or physic and bio.
- Grades are counted as per individual grades unlike combined
sciences is counted as 1 subject.
eg. Physic - A1
Chemistry - A1
Bio - A1
- Can score A's if u understand well.
- If you dont understand or doesnt score well in pure, you can drop
to combined sciences. ( have quite a few class mates who take pure
sciences and later drop to take combined sciences)
- People say is better .
that my 2 cents of ideas. hope u understand
finally, make the right decision, normally the school will decide
which one u will take, which determines that Your results must be
good in order to go to pure sciences class.
Study hard ! 
