A stone projected vertically up from the ground reaches a height `y` in its path at `t_(1)` seconds and after further `t_(2)` seconds reaches the ground. The height `y` is equal to
A. `(1)/(2) g (t_(1) + t_(2))`
B. `(1)/(2)g (t_(1) + t_(2))^(2)`
C. `(1)/(2) g t_(1) t_(2)`
D. `g t_(1) t_(2)`