A minor is the relative minor, it can be called the aeolian mode, built on the 6th degree of the scale. So in C major it’s A minor. Same notes, just starting on the A.
Is this some sort of test? I thought I’d had enough of H&T tests during my MMus.
Are you going to admit that the key is D major? I mean consider the A7sus4 chord, with an A and F# played on the bass, that implies, to me at least D major: D, E, F#, G, A. There’s no C# because that would spoil the suspended and open quality that they’re going for using the sus chord.