もっともらしいじゃありません
尤もらしいじゃありません
mottomorashiija arimasen

Desu Copula
i-Adjective
Negation Auxiliary

The polite negative form of もっともらしい

1. It doesn't seem so.; That doesn't seem likely.; It's unlikely.

Negative
Polite
Terminal Form
Usually Written in Kana