Credible means easy to believe. If something is likely; why should it not be credible?
also if it comes from a credible source, I would assume that it's credible.
Now, we're left with the choice between interested and disinterested party: among the two the interested party is more likely to make false claims, as they can benefit from them: so I think that answer <span>d.<em> the claimant is an interested party</em>
is the correct one. </span>
The word that goes, or better expressed, is a synonym for edge is: precipice because it has both the literal and metaphorical connotations just as edge does. It means a very steep or overhanging place, like in a cliff, and it also means to be at the brink of a situation just like edge.
The other words do not match both or any of the definitions of edge.
Do is a command, in the past instructing.
Does is in the present, currently doing.
