If you are doing tripple then don't as it will be on the same day as unit 3. If not you could try. I got A in biology and chemistry and B in physics! Didn't count on having a whole question on plum pudding! Good luck!
Well there is not harm in resitting. I got a B in my Biology however I was supposed to get an A* so I am definitely resitting. Just think, you can't lose anything from resitting an exam as long as you leave time to revise for other subjects too.
Listen 'M' I'm sorry that it is so impossible for you to fathom that a person in this vast entity would need advise, I'm sorry that we all are not as intellectual as someone who has the capacity to only type their initials when asked for a name. Oh, incase you haven't noticed you internet warrior this is a asking forum, not a 'post sarcastic ignoramus comment' box. Therefore, I recommend you focus on your a levels and good day.