UPSC is a 3 stage selection process involving Prelims, Mains and Interview which tests your personality test. Prelims has 2 Papers namely General Studies and CSAT.
General Studies has Current Events, History of India and Indian National Movement, Indian and World Geography, Indian Polity and Governance, Economic and Social Development, Environmental Ecology, Biodiversity and Climate Change and General Science.
CSAT has Comprehension, Interpersonal skills including communication skills, Logical Reasoning and Analytical ability, Decision making and problem solving, General Mental Ability, Basic numeracy and Data Interpretation.
Regarding the subjects that you can pursue in Graduation, Candidates who studied, Political Sciences, Life Sciences are the ones who were most shortlisted for Mains. This has got nothing to do with subject preference but mostly because the topics covered in these streams are also beneficial for studying Prelims and Mains. SO you can study Political Sciences or Life Sciences.
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