Preeti reached the metro station and found that the escalator was not working. She walked up the stationary escalator in time `t_1`. On other days, if the remains stationary on the moving escalator, then the escalator takes her up in time `t_2`. The time taken by her to walk up on the moving escalator will be :

Options

A. `(t_1t_2)/(t_2-t_1)`
B. `(t_1t_2)/(t_2+t_1)`
C. `t_1-t_2`
D. `(t_1+t_2)/2`