長壁 おさかべ しき採炭 さいたんじゃなかったです
osakabeshiki saitanjanakattadesu

Noun
Desu Copula

The polite, past negative form of 長壁式採炭

1. Was not longwall mining.; Wasn't longwall mining.

Past/Perfective
Negative
Polite
Casual Register
Mining