[单选题]
A projectile is fired with a launch angle α above the horizontal and an initial velocity of 40 $m\,s^{-1}$ towards a cliff that rises 300 m above the plane of projection. The cliff is 120 m from the launch point.
Assuming that air resistance has no effect on the motion, then the time of flight taken by the projectile to reach the plane of the cliff, is given by
A. t=3 s
B. t=7.5 s
C. t=$\frac{4}{cos}$
D. t=$\frac{3}{cos}$
