1. First, you need to find the original file you quoted. This is usually your main reference, that is, the literature you quoted directly.
In your paper, you need to mark the quotation with brackets and numbers. For example, if you are quoting a passage from an author, you can mark it like this: "(Smith, 20 15)". Here "Smith" is the author's name and "20 15" is the year of publication.
When you need to refer to this document again, you need to add a letter after the brackets to indicate that this is your second reference. For example, you can label it like this: "(Smith, 20 15a)". The "A" here means that this is your second quotation.
If you need to refer to the same document three times, you can add more letters after the letters. For example, you can label it like this: "(Smith, 20 15ab)". The "ab" here means that this is your three quotations.
If you need to quote several documents published by the same author in the same year, you can add a lowercase letter after the year to distinguish these documents. For example, it can be labeled as "(Smith, 20 15a)" and "(Smith, 20 15b)".
When you quote the second quotation in the text, you need to add the page number after the brackets. For example, you can label it like this: "(Smith, 20 15a, page 23)". "p.23" here means that this is the specific page number you quoted in Smith's literature.
7. Finally, you need to list all the references in the reference list. In this list, you should arrange the author's name in alphabetical order, followed by the publication year and page number. For the second quotation, you should use the format you marked in the text.
The above is the correct way to mark the second citation of academic papers in English. Remember, correctly quoting can not only avoid plagiarism, but also let readers know what existing academic achievements your research is based on.