Radius & Circumference
The compass opening produces the radius of a circle, which is the distance from the centre to the outer ring, (circumference).
Radius of One
Regardless of how large we make the initial compass opening, we always call that distance 1 (ONE).
The diameter is the distance across the centre of the circle.
Correct answer: 2
As the radius is standardised to the value of 1, adding up double the length will be 2, the diameter of the circle.