Quality Assurance aims at
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Testing New applications for successful implementation of New Functionalities
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Testing Existing applications for successful implementation of Existing Functionalities
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Both (a) and (b)
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Either (a) or (b)
Quality Assurance covers both new and existing applications - it's about ensuring quality across all software, not just new developments or just maintenance. QA activities include testing both newly implemented features and verifying existing functionalities continue to work correctly.
Quality Assurance is a process-oriented discipline focused on verifying that software—whether newly built or already in production—correctly implements its intended functionality before/after change. It doesn't only apply to brand-new features (option a alone) nor only to regression of existing ones (option b alone); QA processes (test planning, execution, defect management) apply uniformly to both new development and maintenance/regression testing of existing functionality. Hence 'Both (a) and (b)' is correct — 'Either/or' is wrong because QA isn't a choice between the two, it necessarily spans both.