The use of et al, is appropriate when the A. source has more than two authors. B. publication date isn't known. C. author's name isn't known. D. source has more than three authors.

D. source has more than three authors.

Explanation:

'et al.' is used in the in-text citations where three or than than three authors are to be mentioned for a particular work. The meaning of the Latin word 'et al.' is 'and others'. The last name of the first author is written and then 'et al.' is added to it. A comma (,) is then added along with the year of the publication of the work. In this way, the in-text citation is shortened by just adding the last name of the authors.

i believe it is the first choice (1.)

because the major theme is(“both the wild and civilization have rules.”)

and also as u said,( based on what buck learns within the call of the wild, "both the wild and civilization have rules".this is true of humans within society as well.