Answer: The answer is (b).

Step-by-step explanation: Let us consider a circle with centre "O" and radius OA=OB=r units. We know that the circumference of a circle is
so the circumference of Circle 'C' is given by
Also, let us central angles of equal size of 'n°', the the number of sectors formed is given by

Now, the formula for arc length of a sector is given by

∴

Thus, (b) is the correct option.