Which word in the sentence does the underlined phrase explain? the house, a historic landmark, was more than 100 years old. a. years b. house c. old d. than

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.