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You put a comma (even if a period is intended) when you are going to follow the quote mark with a tag or any other writing. You put a period if the end of the quote is also the end of the sentence.
Answer
#4: Attribution notice removed
Source: https://writers.stackexchange.com/a/31402 License name: CC BY-SA 3.0 License URL: https://creativecommons.org/licenses/by-sa/3.0/
#3: Attribution notice added
Source: https://writers.stackexchange.com/a/31402 License name: CC BY-SA 3.0 License URL: https://creativecommons.org/licenses/by-sa/3.0/