The formula to find the arc length L is
L = r*theta
where r is the radius and theta is the central angle in radians (this formula will not work if theta is in degrees)
If the central angle is 1 radian, then theta = 1 and
L = r*theta
L = r*1
L = r
So the arc length is the same as the radius
Answer: Choice A) The radius of the circle