If R is a relation from a finite set A having m elements to a finite set B having n elements, then the number of relations from A to B is

• A

  $2^{\mathrm{mn}}$

• B

  $2^{\mathrm{mn}}-1$

• C

  $2\mathrm{mn}$

• D

  ${\mathrm{m}}^{\mathrm{n}}$