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A great explanation: http://www.quickanddirtytips.com/education/grammar/how-to-use-quotation-marks Notice that American form can be different than UK.
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#3: Attribution notice added
Source: https://writers.stackexchange.com/a/21540 License name: CC BY-SA 3.0 License URL: https://creativecommons.org/licenses/by-sa/3.0/