A straw 6 cm long floats on water. The water film on one side has surface tension of 50 dyne/cm. On the other side, camphor reduces the surface tension to 40 dyne/cm. The resultant force acting on the straw is

• A

  $\text{60 dyne }$

• B

  $10 dyne$

• C

  $\left(\frac{50}{6}-\frac{40}{6}\right)\text{ dyne }$

• D

  $90 dyne$