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)`