Final answer:
The most credible source is the results of an internal investigation by a major corporation, posted on the company's website.
Step-by-step explanation:
The most credible source among the given options is A. The results of an internal investigation by a major corporation, posted on the company's website.
This source is the most credible because it is directly from the company conducting the investigation and is posted on their official website. It is likely to provide reliable and accurate information about the internal investigation.
On the other hand, options B, C, and D are all subjective or opinion-based sources. Option B is an opinion article on a political party's website, which may have bias and may not provide a balanced view. Option C is an opinionated book that may present a specific perspective on climate change. Option D is a blog from an activist and Internet personality, which may also have bias and lack credibility.