The Dominant 7th Sound
A major 3rd, then a minor 3rd, then a minor 3rd — and 5 near misses, each a single tone away.
The chord-quality drill loads here.
Built upward, the dominant 7th is a major 3rd, then a minor 3rd, then a minor 3rd — 4 tones in all. In a drill it arrives in a key you did not choose, so the only thing left to listen to is that shape.
Near missesmajor triad, major 7th, minor 7th, major 6th chord and add9 — each one is this chord with a single tone moved, which is why a wrong answer here is almost never random.
It sits in the foundation tier — the answers every later round is measured against.