Hey Alice,
As an aspirant myself I'll do my best to put down the advantages for choosing a particular subject with respect to your question.
I think that indopak history is more thorough but it concides with your Pak. Affairs - compulsory subject, so you can cover a lot of similar topics of both the subjects simultaneously. And U.S. history is a little brief comparatively speaking but it may help you in current affairs paper as well. Moving on towards your second optional pair, law is breif but you need to go through it's content to weigh whether you'd able to do it or not. Gender studies is relatively new and some of it's topic are related to current affairs and essay paper as well, if you find it interesting then go for it. Philosophy is do-able but it really doesn't go with the rest of your subjects. Now, coming towards Psychology, have you studied it before? Because it doesn't go with your prior academic background and seeing this the right opportunity let me also point out that Business ad. in also a very technical subject including; HR, cost accounting, marketing, management, supply chain and etc. So, I hope you have studied it before atleast some of it if not all. Lastly, I would have talked more about law but you didn't mention which law particularly are you interested in.
I hope it helps.

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