$A$ particle of mass $m$ is projected with speed $u$ at angle $\theta$ with the horizontal from the ground. The work done by gravity on it during its upward motion is ..........

• A
  $\frac{m u^2 \cos^2 \theta}{2}$
• B
  $\frac{-m u^2 \sin^2 \theta}{2}$
• C
  $\frac{m u^2 \sin^2 \theta}{2}$
• D
  Zero