Given that

$$ Distance\ between\ A\ and\ B=2000km $$

$$ Distance\ between\ A\ and\ C=1600km $$

$$ Distance\ between\ A\ and\ D=2500km $$

As given in figure above

$$ Distance\ between\ C\ and\ D=900km=300km\times3 $$

and

$$ Distance\ between\ B\ and\ C=1200km=400km\times3 $$

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

$$ \therefore Distance\ between\ B\ and\ D=500km\times3=1500km $$

So Choice E is correct.