Hello,
The three exams that you've mentioned have different exam pattern, but the eligibility criteria is common that is graduation in any discipline from a recognized university(I'm also referring this for RRB Graduate level exams).
People from different background have cracked the above mentioned exams as they have put efforts, so you can also crack any of these exams with BCA degree. During your graduation time period itself, you can go through the syllabus of these exams and start with the subjects involved, with little steps you'll be definitely able to succeed. Going through syllabus, previous year questions, doing mock test regularly and most importantly practice, revision are extremely important in cracking any government exams
Now, coming to your question, if you are particularly interested in cracking one exam among the three, then I'll suggest from the onset, you go with that. As I mentioned, these exams have different pattern, so preparing for all three at one time will become highly difficult for you.
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