Two particles are projected simultaneously in the same vertical plane from the same point, with different speeds `u_(1)` and `u_(2)`, making angles `theta_(1)` and `theta_(2)` respectively with the horizontal, such that `u_(1) cos theta_(1) = u_(2) cos theta_(2)`. The path followed by one, as seen by the other (as long as both are in flight), is
A. a horizontal straight line
B. a vertical straight line
C. a parabola
D. a straight line making an angle `|theta_(1)- theta_(2)|` with the horizontal
