The diameter of a metal  ring is D and coefficient  of linear  expansion is $\mathrm{\alpha }$ . If the temperature  of the ring is  increases by 1°C , the circumference of the ring will increases by 

• A

  $\frac{\mathrm{\pi D\alpha }}{2}$

• B

  $2\mathrm{\pi D\alpha }$

• C

  $\mathrm{\pi D\alpha }$

• D

  ${\mathrm{\pi D}}^2\mathrm{\alpha }$