Which of the following trains is the fastest ?

Answer: Option D

$$\begin{array}{rl}& 25\text{ m/}\sec :\\ & =\left(25\times \frac{18}{5}\right)\text{km/hr }\\ & =90\text{ km/hr}\\ & \text{And, 25 m/}\sec :\\ & =\left(25\times 60\right)\text{ m/}\sec \\ & =1500\text{ m/}\sec \end{array}$$
So, all the three speeds are equal.