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1. Primary source - It is a firsthand evidence of an event or an experiment. It
includes real data, original documents, proofs, account of people involved etc. Thus it gives the details as they occurred.
2. Secondary source - It is written after
an event or an experiment has occurred. It provides different perspectives, analysis and conclusion.
3. Tertiary source - It is a kind of index of all available primary and secondary sources on a topic. Often a tertiary source contains reference to all primary and secondary sources along with a short description.
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