The correct answer is Plausible; Implausible
Argument is a set of words that form declarative sentences, with a broad meaning that the human being expresses when in dialogue.
Plausible is what is reasonable, possible to be done or acceptable.
To say that someone had a plausible argument means that the person had an adequate, credible answer. It does not mean that it was something excellent, or above expectations, but considered reasonable.
