Two particles are projected simultaneously in the same vertical plane, from the with speed `u_(1)` and `u_(2)` at angle of projection `theta_(1)` and `theta_(2)` respectively with the horizontal. The path followed by one, as seen by other (as long as both are in flight), is
A. a vertical straight line
B. a straight line making a constant angle `(ne 90^(@))` with the horizontal
C. a parabola
D. a hyperbola
