A particle projected with an initial velocity $u$ at angle $\theta$ from the ground. The work done by gravity during the time it reaches the highest point $P$ is:
(A) $\frac{-m u^{2} \sin ^{2} \theta}{2}$
(B) $+\frac{m u^{2} \sin ^{2} \theta}{2}$
(C) 0
(D) $+m u^{2} \sin \theta$