The key of C minor
C D E♭ F G A♭ B♭
3 flats: B♭ E♭ A♭. Relative major: The key of E♭ major.
The triads of the key
i
Cm | ii°
D° | III
E♭ | iv
Fm | v
Gm | VI
A♭ | VII
B♭ |
The seventh chords
i7
Cm7 | iiø7
Dm7♭5 | IIImaj7
E♭maj7 | iv7
Fm7 | v7
Gm7 | VImaj7
A♭maj7 | VII7
B♭7 |
In practice the V of a minor key is almost always major, taken from the harmonic minor: G7 (V7), which carries the leading tone B.
C natural minor scale
Open it in the app: 6. Harmony, in C