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 she 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

A

$$\frac{t_1 t_2}{t_2 + t_1}$$

B

$${t_1 - t_2}$$

C

$$\frac{t_1 + t_2}{2}$$

D

$$\frac{t_1 t_2}{t_2 - t_1}$$