If a section of soap bubble (of radius r) through its center is considered, the force on one half due to surface tension is

• A

  $2\mathrm{\pi rT}$

• B

  $4\mathrm{\pi rT}$

• C

  ${\mathrm{\pi r}}^2\mathrm{T}$

• D

  $2\mathrm{T}/\mathrm{r}$