D. most closely match their sweat rates
Oxygen in the air can cause sliced fruit to brown, a process called enzymic browning (an oxidation reaction). Phenols and the enzyme phenolase are found in the cells of the apple, and when these are exposed to oxygen in the air, for example through slicing, the oxygen causes a reaction.
I would say that if she is being mean you can first try to talk it out with her (because relationships may take work sometimes and if she is really important both of you will be willing to put in the work), but if that doesn't go well and you really don't think it is going to work you should go to your other friends or family for support especially if she was a very important part of your life.
