専門 せんもん分野 ぶんやじゃありませんでした
semmombun'yajārimasendeshita

Noun
Desu Copula

The polite, past negative form of 専門分野

1. Was not my specialty.; Was not my field of expertise.; I wasn't a specialist in that.

Past/Perfective
Negative
Polite
Terminal Form