んです => Because, by… N4
Situations and Experiences
そうにない => N2
Potential, Possibility
でなくてなんだろう => It's definitely A (and not something else) N1
Information, Report
ずにはすまない/ないではすまない => A must be done N1
Potential, Possibility
すら,ですら => Even A N1
(Not)only , (Not) even
に[相違「そうい」]ない => No doubt N2
Information, Report
~ます/~ません => Polite, present form N5
Verb suffixes
それはそうと => By the way N2
Miscellaneous
そうだ => Seem, like… N4
Situations and Experiences
そうもない => The chances of A are very low N1
Potential, Possibility
[謙譲語「けんじょうご」] => Humble form of A, humble form of する verbs N4
Honorifics
それでも => Even though A, B N2
Contrast,Surprise