Hello,
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You can persue any stream in your 11 and 12th. There's no particular stream mentioned in the eligibility criteria of BCA. Candidate must have 50% in there +2 in any stream with English as a mandatory subject. But remember it may differ from college to college, the above information is based on the Eligiblity criteria of most the  colleges, but few of the college's may differ it's Eligiblity criteria.