It is correct to introduce the authors of the book as: DuPont, Lonnie, et al.
This is because, according to the MLA style, when a book, journal, or article has three or more authors, the reference must be made with the surname of the first two authors and then present the expression "et al."
As the book presented above has 4 authors, it is correct to introduce them as "DuPont, Lonnie, et al."
It is important to emphasize that a bibliographical reference allows:
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