For this multiple choice, it would be A. But in the real world, the most credible address suffix is either all of them or none of them. It really depends on who the author is and is the organizations website biased or an unbiased. Ask yourself if the organization has an agenda(purpose) for having a website.
Most sites end with .com and therefore a lot of them could be credible or not. Again, it really depends on who the author is, and do they have an agenda. If they do then is their agenda good, or bad. It may also be irrelevant if the agenda is good and bad. So basically, the agenda might not be good or bad. It's neither.
