$A$ parallel beam of light is incident normally on a plane surface absorbing $50\%$ of the light and reflecting the rest. If the incident beam carries $90 \text{ W}$ of power,the force exerted by it on the surface is ($C = 3 \times 10^8 \text{ m/s}$ is the velocity of light in air).

• A
  $4.5 \times 10^{-7} \text{ N}$
• B
  $1.5 \times 10^{-7} \text{ N}$
• C
  $3 \times 10^{-7} \text{ N}$
• D
  $9 \times 10^{-7} \text{ N}$