So,
Let's state everything in terms of meters (m).
The conversion factor between km and m is as follows:
1 km = 1000 m
Therefore, 2 km is 2000 m.
The conversion factor between cm and m is as follows:
100 cm = 1 m
Therefore, 2500 cm is 25 m.
The conversion factor between mm and m is as follows:
1000 mm = 1 m
Therefore, 3000 mm is 3 m.
Here are all the numbers in meters.
2000 m, 25 m, 25 m, 3 m
We can quickly see that 2000 m is the longest distance. It is 2 km.