Final answer:
The best evidence for the Page-Ladson site's age is the discovery of clear evidence of human activity, like stone tools, at the site that can be reliably dated.
Step-by-step explanation:
The best piece of evidence to prove the age of the Page-Ladson site would be d. To prove the age of the site, clear evidence of human activity, usually in the form of stone tools, must be found in a solid place and dated using a reliable dating method. This is because definitive proof of the site's age requires concrete archaeological evidence that can be accurately dated. Options a and b reference other sites and discoveries that do not directly establish the age of the Page-Ladson site, and option c refers to earlier research that would still require concrete artifacts and dating to substantiate the site's antiquity. The Page-Ladson site, with its own historical artifacts and contextual evidence, must be independently dated to validate its age.