a) ethos means credibility to a website, book or anything else.
b) an authoritative site is a website that has reliable information that has a gatekeeper.
c) it is important to have a gatekeeper because if you have a high authority website then the information that goes on to your web page must have real proof the thing happened or that the information you are giving is true. a gatekeeper is the one who helps you with your website making sure that the information you are giving is true. some websites don't have a gatekeeper so the website is not reliable because the information they are giving might not be true.
d) the television news article might be enough information, but it really isn't because the anchor has only a small time to talk about to news information