if `x` and `y` coordinates of a point `P` in `x-y `plane are given by `x=(ucosalpha)t, y=(usinalpha )t-1/2 g t^2 `where `t` is a aprameter and `u,alpha,g`the constants. Then the locus of the point `P` is a parabola then whose vertex is:
A. a circle
B. a parabola
C. an ellipse
D. none of these
