Which one of the following rivers in India was not crossed by Alexander and his army?

Who among the following has described the medieval Indian postal system as of two kinds—the horse-post called ‘Uluq’ and the foot-post called ‘Dawa’?

At which among the following Harappan sites are fire altars found?

Consider the following statements on computation of density :

1. Physiological density can be computed by dividing the total population by the net cultivable area.

2. Agricultural density can be computed by dividing the total agricultural population by the net cultivable area.

3. Population density can be computed by dividing the total population by the total area.

How many of the above statements is/are correct?