Answer:
D is true.
Explanation:
We will use the formula for arc length (in radians) for this problem.
Arc length (s) =

Where
- r is the radius
is the angle in radians
A.
Arc length with
measuring 1 and radius r is:

So, not 2r, as stated. So A is false.
B.
Ratio of arc length to r is:

So, it's not
, B is false.
C.
Arc length, when
and radius is r:

So, C is false.
D.
Setting up ratio of arc length to r as 1 and solving for
:

D is right.