Given that

$$DistancebetweenAandB=2000km$$

$$DistancebetweenAandC=1600km$$

$$DistancebetweenAandD=2500km$$

As given in figure above

$$DistancebetweenCandD=900km=300km\times 3$$

and

$$DistancebetweenBandC=1200km=400km\times 3$$

which are the multiples of 3. then distance between B and D will also be a multiple of 3

$$\therefore DistancebetweenBandD=500km\times 3=1500km$$

So Choice E is correct.