もっともらしいじゃありませんでした
尤もらしいじゃありませんでした
mottomorashiija arimasendeshita

Desu Copula
i-Adjective

The polite, past negative form of もっともらしい

1. It didn't seem likely.; It wasn't plausible.; It didn't appear so.

Past/Perfective
Negative
Polite
Terminal Form
Usually Written in Kana